Method for controlling regenerative braking of vehicle

ABSTRACT

A method for controlling regenerative braking includes determining a natural frequency of vehicle suspension pitch motion according to characteristics of a suspension device of vehicle; providing a filter of removing or passing a natural frequency component of the vehicle suspension pitch motion to a control unit; determining, by the control unit, a required regenerative braking force command based on vehicle driving information collected during driving; determining, by the control unit, a final front wheel regenerative braking force command and a final rear wheel regenerative braking force command through a filtering process using the filter from the determined required regenerative braking force command; and controlling, by the control unit, a regenerative braking force applied to a front wheel and a rear wheel by a driving device for driving the vehicle according to the determined final front wheel regenerative braking force command and final rear wheel regenerative braking force command.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2022-0035718 filed on Mar. 3, 2022, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE PRESENT DISCLOSURE

FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to a method for controlling aregenerative braking force of a vehicle. More particularly, it relatesto a method for resolving problems of a phenomenon of repeatedoccurrence of wheel slip caused by longitudinal load movement anddeterioration of wheel slip control performance by reflecting pitchmotion characteristics and longitudinal load movement information of avehicle in real time in advance to control a regenerative braking forceof the vehicle.

DESCRIPTION OF RELATED ART

Despite the recent introduction of various electronic control devices toa vehicle, motion of the vehicle is ultimately limited due to the limitof frictional force on a road surface. A reason therefor is that motionof the vehicle is obtained through frictional force with respect to theroad surface through a tire. Therefore, how effectively the frictionalforce may be used is an important factor in determining the motion ofthe vehicle.

To effectively use the frictional force, it is important to control thefrictional force which may be provided by the road surface so that adriving force and a regenerative braking force of the wheel do notexceed the frictional force. Here, the frictional force which may beprovided by the road surface is complexly affected by road surfacecharacteristics, longitudinal/lateral tire slip amount, tire verticalload, etc. Among these factors, the tire vertical load is a factor thatmost directly affects the frictional force on the road surface.

In general, as a method of using frictional force, it is known to use anelectronic control device such as an anti-lock braking system (ABS) anda traction control system (TCS) to limit tire slip. However, controlmethods of the ABS and the TCS have disadvantages in that those methodsdo not effectively exhibit slip control performance due to a problem ofwheel speed signal processing, etc. for prevention of control cycledelay or malfunction.

According to the recent trend of wheel slip control strategies inelectrified vehicles, many methods have been proposed to use the torqueand speed of a motor based on fast motion of the motor rather than usinga vehicle body reference speed and a wheel speed.

This strategy has an advantage in that an absolute speed or a referencespeed of the vehicle is not required, and thus may be effective in ane-4WD (4WD: Four Wheel Drive) system. However, unless a controloperation is performed to reflect information related to suspensionpitch motion and the tire vertical load changed by the suspension pitchmotion in advance, a situation requiring driving force reduction controlmay be repeatedly encountered due to limitations of feedback control.

For example, when a driving force of a front wheel is generated, avehicle pitch angle increases, and then a vertical load of the frontwheel decreases, causing tire slip at the front wheel. At the instanttime, when the TCS is operated to reduce the driving force of frontwheel, the tire slip amount of the front wheel is reduced and the pitchangle of the vehicle is reduced, so that the vertical load of the frontwheel may be ensured again. However, when the driving force of the frontwheel is subsequently increased, the vertical load of the front wheeldecreases again while the pitch angle of the vehicle increases again,and thus tire slip of the front wheel may occur again.

The information included in this Background of the present disclosure isonly for enhancement of understanding of the general background of thepresent disclosure and may not be taken as an acknowledgement or anyform of suggestion that this information forms the prior art alreadyknown to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present disclosure are directed to providing amethod configured for resolving problems of a phenomenon of repeatedoccurrence of wheel slip caused by longitudinal load movement anddeterioration of wheel slip control performance by reflecting pitchmotion characteristics and longitudinal load movement information of avehicle in real time in advance to control a regenerative braking forceof the vehicle.

The object of the present disclosure is not limited to the objectmentioned above, and other objects not mentioned herein may be clearlyunderstood by those of ordinary skill in the art to which an exemplaryembodiment of the present disclosure belongs (hereinafter referred to as“person of ordinary skill”) from the description below.

Various aspects of the present disclosure are directed to providing amethod for controlling regenerative braking of a vehicle includingdetermining a natural frequency of vehicle suspension pitch motionaccording to characteristics of a suspension device of the vehicle,providing a filter configured for removing or passing a naturalfrequency component of the vehicle suspension pitch motion to a controlunit of the vehicle, determining, by the control unit, a requiredregenerative braking force command based on vehicle driving informationcollected during vehicle driving, determining, by the control unit, afinal front wheel regenerative braking force command and a final rearwheel regenerative braking force command through a filtering processusing the filter from the determined required regenerative braking forcecommand, and controlling, by the control unit, a regenerative brakingforce applied to a front wheel and a rear wheel of the vehicle by adriving device for driving the vehicle according to the determined finalfront wheel regenerative braking force command and the determined finalrear wheel regenerative braking force command.

Other aspects and exemplary embodiments of the present disclosure arediscussed infra.

The above and other features of the present disclosure are discussedinfra.

The methods and apparatuses of the present disclosure have otherfeatures and advantages which will be apparent from or are set forth inmore detail in the accompanying drawings, which are incorporated herein,and the following Detailed Description, which together serve to explaincertain principles of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing a pitch angle in a vehicle;

FIG. 2 is a block diagram illustrating a configuration of an apparatusof performing a regenerative braking control process according tovarious exemplary embodiments of the present disclosure;

FIG. 3 is a flowchart illustrating a regenerative braking controlprocess of the vehicle according to an exemplary embodiment of thepresent disclosure;

FIG. 4 is a diagram illustrating that a pitch angle or a vertical loadmay be determined using a transfer function in an exemplary embodimentof the present disclosure;

FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, FIG. 5F, FIG. 5G, and FIG.5H are diagrams for describing various examples in which a final frontwheel regenerative braking force command and a final rear wheelregenerative braking force command are obtained using a naturalfrequency removal filter in an exemplary embodiment of the presentdisclosure;

FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E and FIG. 6F are diagrams fordescribing various examples in which a final front wheel regenerativebraking force command and a final rear wheel regenerative braking forcecommand are obtained using a natural frequency enhancement (pass) filterin an exemplary embodiment of the present disclosure;

FIG. 7 and FIG. 8 are diagrams for comparing a conventional wheel slipcontrol state with a regenerative braking control state of the presentdisclosure; and

FIG. 9 , FIG. 10 and FIG. 11 are diagrams for describing an effect ofregenerative braking control according to an exemplary embodiment of thepresent disclosure.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of the presentdisclosure. The specific design features of the present disclosure asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent disclosure(s), examples of which are illustrated in theaccompanying drawings and described below. While the presentdisclosure(s) will be described in conjunction with exemplaryembodiments of the present disclosure, it will be understood that thepresent description is not intended to limit the present disclosure(s)to those exemplary embodiments of the present disclosure. On the otherhand, the present disclosure(s) is/are intended to cover not only theexemplary embodiments of the present disclosure, but also variousalternatives, modifications, equivalents and other embodiments, whichmay be included within the spirit and scope of the present disclosure asdefined by the appended claims.

Meanwhile, in an exemplary embodiment of the present disclosure, eventhough terms such as “first”, “second”, etc. may be used to describevarious elements, the elements are not limited by these terms. Theseterms are only used to distinguish one element from another. Forexample, within the scope not departing from the scope of the rightsaccording to the concept of the present disclosure, a first element maybe referred to as a second element, and similarly, the second elementmay be referred to as the first element.

When an element is referred to as being “coupled” or “connected” toanother element, the element may be directly coupled or connected to theother element. However, it should be understood that another element maybe present therebetween. In contrast, when an element is referred to asbeing “directly coupled” or “directly connected” to another element, itshould be understood that there are no other elements therebetween.Other expressions for describing a relationship between elements, thatis, expressions such as “between” and “immediately between” or “adjacentto” and “directly adjacent to”, should be interpreted similarly.

Like reference numerals refer to like elements throughout. Theterminology used herein is for the purpose of describing theembodiments, and is not intended to limit the present disclosure. In thepresent specification, a singular expression includes the plural formunless the context clearly dictates otherwise. Referring to expressions“comprises” and/or “comprising” used in the specification, a mentionedcomponent, step, operation, and/or element does not exclude the presenceor addition of one or more other components, steps, operations, and/orelements.

Various embodiments of the present disclosure relates to a method forcontrolling regenerative braking of a vehicle, and provides a methodconfigured for resolving problems of a phenomenon of repeated occurrenceof wheel slip caused by longitudinal load movement and deterioration ofwheel slip control performance by reflecting pitch motioncharacteristics and longitudinal load movement information of a vehiclein real time in advance to control a regenerative braking force of thevehicle.

In an exemplary embodiment of the present disclosure, to control aregenerative braking force applied to a driving wheel by a drivingdevice (that is, a motor) of the vehicle, information related to atransfer function TF, which takes a variable representing a drivingstate of the vehicle as input, and determines and outputs stateinformation related to pitch motion of the vehicle, is used. Here, thedriving wheel includes both a front wheel and a rear wheel of thevehicle. Furthermore, in an exemplary embodiment of the presentdisclosure, the vehicle is a vehicle in which regenerative braking forcemay be applied to both the front wheel and the rear wheel.

In an exemplary embodiment of the present disclosure, the regenerativebraking force is a force applied to the driving wheel by the motor,which is the driving device configured for driving the vehicle, and maybe the sum of forces acting between a road surface and a tire of thedriving wheel, which is connected to the motor to be able to transmitpower.

The regenerative braking force may be a force by torque applied to thedriving wheel by the motor, which is the driving device of the vehicle.In the present instance, the torque applied to the driving wheel becomesregenerative braking torque applied by the motor. Furthermore, theregenerative braking force is a force that decelerates the vehicle andnot a force that accelerates the vehicle (driving force), and refers toa braking force by the regenerative braking torque applied to thedriving wheel by the motor to decelerate the vehicle.

Furthermore, in an exemplary embodiment of the present disclosure,control of the regenerative braking force may be performed bycontrolling the operation and output of the motor, which is the drivingdevice, or by controlling the torque applied to the driving wheel. Inthe following description, “regenerative braking force” and“regenerative braking force command” may be replaced with “regenerativebraking torque” and “regenerative braking torque command”.

A basic concept of a regenerative braking control method according to anexemplary embodiment of the present disclosure is to use state andcharacteristic information related to pitch motion of the vehicle. Theexisting regenerative braking control method for suppressing wheel slipis a feedback control method that corrects the regenerative brakingforce after wheel slip has already occurred. However, in an exemplaryembodiment of the present disclosure, before wheel slip occurs, themagnitude of the regenerative braking force is adjusted to correspond tothe pitch motion by use of the state and characteristic informationrelated to the pitch motion of the vehicle.

As the state and characteristic information related to the pitch motionof the vehicle, mention may be made of the tire vertical load and thepitch angle of the vehicle. of the vehicle load and the pitch angle, thetire vertical load is the most direct factor for determining a limit oftraction between the road surface and the tire. As the tire verticalload increases, the available traction increases, making it difficult tocause wheel slip. As the tire vertical load decreases, the availabletraction decreases, making it vulnerable to wheel slip.

There are many reasons for the change in the tire vertical load, and itis difficult to control the driving force and the regenerative brakingforce while considering all the reasons including the change due todisturbance. Therefore, at least the change in the tire vertical loadcaused by the regenerative braking force itself, except for the changedue to disturbance, is worth considering in a regenerative brakingcontrol process.

Furthermore, when a regenerative braking force is generated in thevehicle, the pitch moment is generated due to a difference between thecenter of gravity and a pitch center of the vehicle, and the pitchmotion of the vehicle is excited. At the instant time, a pitch angle isgenerated by mechanical characteristics of a suspension device and avehicle body.

In general, a pitch angle increases when a vehicle accelerates, and astate of the vehicle at the instant time is referred to as nose-upmotion or a squat state. Furthermore, when the vehicle decelerates, thepitch angle decreases, which is referred to as nose-down motion or adive state.

When such pitch motion of the vehicle occurs, the suspension device ofthe vehicle is contracted or stretched. As a result, a spring or adamper of the suspension device is displaced, and the tire vertical loadis affected.

In an exemplary embodiment of the present disclosure, only a suspensionpitch angle and not a road surface pitch angle, is considered as thepitch motion, and definition of the suspension pitch angle isillustrated in FIG. 1 . FIG. 1 is a diagram for describing a pitch anglein the vehicle.

As illustrated in the figure, the pitch angle in the vehicle may bedivided into a suspension pitch angle and a road surface pitch angle,and the sum of the suspension pitch angle (absolute value) and the roadsurface pitch angle (absolute value) may be defined as a summed pitchangle.

When a stroke difference occurs between a front wheel suspension deviceand a rear wheel suspension device, so that the front wheel suspensiondevice is more rebounded (stretched) than the rear wheel suspensiondevice, and the rear wheel suspension device is more bumped (contracted)than the front wheel suspension device, the suspension pitch angle maybe defined as a position (+) suspension pitch angle. At the instanttime, a suspension pitch angle of a vehicle state illustrated in FIG. 1is a positive value.

The road surface pitch angle corresponds to a longitudinal inclinationof the vehicle due to an inclination of the road surface, and thesuspension pitch angle represents a longitudinal (pitch direction)inclination of the vehicle caused by extending or contraction of thefront and rear wheel suspension devices. In a typical vehicle, the roadsurface pitch angle (road gradient) may be detected through alongitudinal acceleration sensor.

Information related to the suspension pitch angle (suspension pitchangle information) illustrated in FIG. 1 in the vehicle is informationindicating a pitch direction vibration state of the vehicle according toa stroke change of the front suspension device and the rear suspensiondevice during vehicle driving, which may be obtained through a sensor ofthe suspension device, or may be estimated based on informationcollected through a sensor in the vehicle.

A method of obtaining suspension pitch angle information through asensor of a suspension device in a vehicle is known technology. Forexample, by use of a position sensor of the front wheel suspensiondevice and a position sensor of the rear wheel suspension device tocompare positions of the front wheel and the rear wheel based on signalsof the position sensors, it is possible to determine suspension pitchangle information of the vehicle.

Furthermore, a method of estimating suspension pitch angle informationis known technology. That is, there is a known method of obtaining apitch angle by integrating a signal of a pitch rate sensor orkinematically estimating the pitch angle based on a longitudinal orvertical direction acceleration sensor value.

Furthermore, there are a method of estimating the pitch angle through asuspension device model-based observer, a method of determining thepitch angle through a wheel speed information and driving force(regenerative braking force) information model, a method of observingpitch angle information using a sensor fusion method by integratingthese methods, etc.

The vehicle state illustrated in FIG. 1 may be referred to as a state inwhich the suspension pitch angle indicates a positive (+) valuedirection. In the present instance, the vehicle state may be referred toas a squat state based on the suspension pitch angle. Contrary to FIG. 1, when the suspension pitch angle indicates a negative (−) valuedirection, the vehicle state may be referred to as a dive state based onthe suspension pitch angle.

Furthermore, the vehicle state illustrated in FIG. 1 is a state in whichthe vehicle body is tilted backward, and thus may be referred to as asquat state based on the vehicle body. The squat state (body squatstate) with respect to the vehicle body may be referred to as a state inwhich the vehicle body is tilted backward based on a non-tiltedhorizontal line (inclination angle=0°).

Furthermore, a state in which the vehicle body is tilted forward may bereferred to as a dive state with respect to the vehicle body, and thevehicle body dive state may be referred to as a state in which thevehicle body is tilted forward with respect to the horizontal line.

As described above, in the vehicle state illustrated in FIG. 1 , thesquat state may be induced based on the suspension pitch angle when thevehicle is accelerated, and the vehicle dive state may be induced basedon the suspension pitch angle when the vehicle is decelerated.

At the present time, the change in the vehicle suspension pitch motionor the longitudinal load movement of the vehicle due to the change inthe state of the suspension device appears according to characteristics(suspension device characteristics of the vehicle) determined byvehicle-specific suspension device setting. Here, the setting includesall of the spring stiffness, damping force, bushing stiffness,suspension arm flow geometry, etc. of the suspension device.

Due to these characteristics, suspension pitch motion such as dive (nosedown)/squat (nose up) of the vehicle is generated while exhibiting thecharacteristics determined by the above setting. Here, thecharacteristics mean motion with a specific natural frequency.

Accordingly, a principle of the present disclosure is modeling thevehicle suspension pitch motion or longitudinal load movement determinedby the setting and characteristics of the suspension device of thevehicle, removing a frequency component corresponding to a naturalfrequency of the present model from a regenerative braking force commandusing a filter, generating a regenerative braking force command thatdoes not excite the suspension pitch motion or longitudinal loadmovement of the vehicle as much as possible, and controlling theregenerative braking force by the motor of the vehicle using the presentregenerative braking force command, preventing wheel slip.

Alternatively, on the other hand, by further enhancing the frequencycomponent corresponding to the natural frequency using a filter in aregenerative braking force command, an appropriate regenerative brakingforce is applied to a driving axle of one of the front wheel and therear wheel having a traction ensured by load movement, ensuring brakingperformance within a range within which wheel slip may be suppressed.

Next, an apparatus of controlling regenerative braking will be describedtogether with a detailed description of the regenerative braking controlmethod. FIG. 2 is a block diagram illustrating a configuration of anapparatus of performing a regenerative braking control process accordingto various exemplary embodiments of the present disclosure, and FIG. 3is a flowchart illustrating a regenerative braking control process ofthe vehicle according to an exemplary embodiment of the presentdisclosure.

Referring to FIG. 2 , an apparatus of controlling regenerative brakingaccording to an exemplary embodiment of the present disclosure includesa first control unit 20 that determines a required regenerative brakingforce command (required torque command) from vehicle drivinginformation, and determines and outputs a front wheel regenerativebraking force command and a rear wheel regenerative braking forcecommand distributed according to a front and rear wheel powerdistribution ratio from the required regenerative braking force command,a second control unit 30 that is configured to control a regenerativebraking force applied to the front and rear wheels of the vehicleaccording to the front wheel regenerative braking force command and therear wheel regenerative braking force command received from the firstcontrol unit 20, and a front wheel driving device and a rear wheeldriving device as a driving device 40 for driving the vehicle, anoperation (generation and application of the regenerative braking force)thereof is controlled by the second control unit 30.

Here, the front wheel regenerative braking force command is a commandgenerated and output by the first control unit 20 to apply aregenerative braking force (regenerative braking torque) to the frontwheel and a front axle among the driving wheels and driving axles of thevehicle, and the rear wheel regenerative braking force command is acommand generated and output by the first control unit 20 to apply aregenerative braking force to the rear wheel and a rear axle. The frontwheel regenerative braking force command and the rear wheel regenerativebraking force command may be torque commands, and at the instant time, avalue of each regenerative braking force command becomes a value of theregenerative braking torque distributed to a corresponding driving wheeland a driving axle.

Furthermore, the front wheel regenerative braking force command and therear wheel regenerative braking force command may be a torque commandfor the front wheel driving device and a torque command for the rearwheel driving device, respectively. Because the driving device of thevehicle is a motor, both the front wheel torque command and the rearwheel torque command become motor torque commands.

In the following description, “front wheel regenerative braking forcecommand” may be replaced with “front wheel regenerative braking torquecommand”, “front axle regenerative braking torque command”, or “frontaxle regenerative braking force command”. Furthermore, “rear wheelregenerative braking force command” may be replaced with “rear wheelregenerative braking torque command”, “rear axle regenerative brakingtorque command”, or “rear axle regenerative braking force command”.

The regenerative braking force control method according to an exemplaryembodiment of the present disclosure may be applied to a 4WD vehicle inwhich the front wheel and rear wheel are driven by independent drivingdevices, respectively, and specifically, may be applied to a vehicle towhich an e-4WD system including motors as both the front wheel drivingdevice and the rear wheel driving device is applied, that is, an e-4WDvehicle.

In the example of the e-4WD vehicle, the first control unit 20determines a required regenerative braking force command for driving thevehicle from vehicle driving information, and distributes the requiredregenerative braking force command to the front wheel regenerativebraking force command and the rear wheel regenerative braking forcecommand according to a determined front and rear wheel powerdistribution ratio.

The required regenerative braking force command may be a required torquecommand determined and generated based on vehicle driving informationcollected in real time while driving in a normal vehicle. In the presentinstance, the first control unit 20 may be a control unit thatdetermines and generates a required torque command based on vehicledriving information in a normal vehicle, that is, a vehicle control unit(VCU).

A method of determining and generating a required torque command in anormal vehicle and a process thereof are well-known in the art, and thusa detailed description thereof will be omitted.

Furthermore, a filter applied to the regenerative braking force commandis configured in the first control unit 20, and the first control unit20 applies the filter to the regenerative braking force command tocorrect the regenerative braking force command, and generates andoutputs a final regenerative braking force command (final front wheelregenerative braking force command and final rear wheel regenerativebraking force command) undergoing a correction process by the filter.

The first control unit 20 performs correction for selectively applying afilter to the required regenerative braking force command beforedistribution, the distributed front wheel regenerative braking forcecommand, or the distributed rear wheel regenerative braking forcecommand, as will be described later. In the present instance, the firstcontrol unit 20 may additionally correct the regenerative braking forcecommand to which the filter is not applied, considering that correctionusing the filter is performed.

Furthermore, the first control unit 20 determines the final front wheelregenerative braking force command and rear wheel regenerative brakingforce command through the above correction process including applicationof the filter to the regenerative braking force command, and outputs thedetermined final front wheel regenerative braking force command and rearwheel regenerative braking force command to the second control unit 30.

As described above, the final front wheel regenerative braking forcecommand and the final rear wheel regenerative braking force commanddetermined and output by the first control unit 20 are finalregenerative braking force commands undergoing a correction process by afilter to be described later. The correction process by the filter meansa predetermined filtering process using the filter. The use of thefilter and the filtering process will be described in detail later.

Furthermore, when the final front wheel regenerative braking forcecommand (final front wheel torque command) and the final rear wheelregenerative braking force command (final rear wheel torque command) aredetermined by the first control unit 20 and output, the second controlunit 30 is configured to control the regenerative braking force(regenerative braking torque) applied to the front wheel and rear wheelaccording to the final front wheel regenerative braking force commandand the final rear wheel regenerative braking force command output fromthe first control unit 20.

In the present instance, the second control unit 30 may control theoperations of the front wheel driving device (front wheel motor) and therear wheel driving device (rear wheel motor), each of which is thedriving device 40 of the vehicle, according to the final regenerativebraking force command output from the first control unit 20. As aresult, the regenerative braking force (regenerative braking torque) byeach controlled driving device 40 is transmitted to the front wheel andrear wheel, each of which is a driving wheel 60, through a reducer (ortransmission) 50, so that the vehicle may be decelerated.

The second control unit 30 may be a motor control unit (MCU) that isconfigured to control the regenerative operation of the motor, which isthe driving device 40, through an inverter according to a regenerativebraking force command (regenerative braking torque command) in a normalmotor-driven vehicle.

In the above description, a control subject includes the first controlunit and the second control unit. However, a regenerative brakingcontrol process according to an exemplary embodiment of the presentdisclosure may be performed by one integrated control element instead ofa plurality of control units.

The plurality of control units and the one integrated control elementmay all be collectively referred to as a control unit, and theregenerative braking control process of the present disclosure describedbelow may be performed by the present control unit. That is, the controlunit may collectively refer to both the first control unit and thesecond control unit.

The required regenerative braking force command (required regenerativebraking torque command) determined by the first control unit 20 isdetermined and generated based on vehicle driving information collectedin real time while driving in the vehicle, and the vehicle drivinginformation may be sensor detection information detected by a sensor 10and input to the first control unit 20 through a vehicle network.

The sensor 10 detecting the vehicle driving information may include abrake pedal sensor (BPS) detecting a brake pedal input value of thedriver, a sensor configured for detecting a drive system speed, and asensor configured for detecting a vehicle speed.

The drive system speed may be a rotation speed of the driving device 40(driving device speed), a rotation speed of the driving wheels 60 (wheelspeed or driving wheel speed), or a rotation speed of a driveshaft(driveshaft speed).

Here, the rotation speed of the driving device may be a rotation speedof the motor (motor speed). In the present instance, the sensorconfigured for detecting the drive system speed may be a sensorconfigured for detecting a speed of the motor, which may be a resolverfor detecting a position of a rotor of the motor. Alternatively, thesensor configured for detecting the drive system speed may be a wheelspeed sensor configured for detecting a rotation speed (wheel speed) ofthe driving wheel or a sensor configured for detecting a rotation speedof the driveshaft.

Furthermore, the sensor configured for detecting the vehicle speed mayalso be a wheel speed sensor. Obtaining vehicle speed information from asignal of the wheel speed sensor is a well-known technology in the art,and thus a detailed description thereof will be omitted.

As the vehicle driving information detected by the sensor 10 and fordetermining the required regenerative braking force command by the firstcontrol unit 20, it is possible to selectively use a brake pedal inputvalue (BPS value) of the driver, a speed (rotation speed) of the drivingdevice, a vehicle speed, etc. In the vehicle driving information, thebrake pedal input value may be referred to as driver driving inputinformation, and the speed and vehicle speed of the driving device 40may be referred to as vehicle state information.

Alternatively, the vehicle driving information may be informationdetermined by the first control unit 20 itself or may be information(for example, required regenerative braking force information orrequired torque information) input to the first control unit 20 throughthe vehicle network from another control unit (for example, ADAS controlunit) in the vehicle.

Furthermore, in the exemplary embodiment of the present disclosure, thesensor 10 may further include a sensor of the suspension device foracquiring suspension pitch angle information. Here, the sensor of thesuspension device for acquiring the suspension pitch angle informationmay include the position sensor of the front wheel suspension device andthe position sensor of the rear wheel suspension device.

As described above, a method for obtaining suspension pitch angleinformation through a sensor of a suspension device is known technology.For example, suspension pitch angle information of the vehicle may bedetermined by comparing the positions of the front wheel and the rearwheel based on a signal from the position sensor.

Furthermore, as described above, the suspension pitch angle, etc. may beobtained by an estimation process determined based on informationcollected from the vehicle through a sensor, etc. Because an estimationmethod thereof is a well-known technical item at the level of thoseskilled in the art, a detailed description thereof will be omitted.

Meanwhile, while the vehicle is accelerating, suspension pitch motion ofthe vehicle occurs in a nose-up (squat) direction, and at the instanttime, the load is transferred to the rear of the vehicle. Therefore,when compared to a neutral state of the load (stationary state), thevertical load of the front axle decreases, making it easy to cause wheelslip, and the vertical load of the rear axle increases, making itdifficult to generate wheel slip.

Therefore, at the instant time, in the case of the front wheel and thefront axle, it is preferable to remove the natural frequency componentof the vehicle suspension pitch motion from the driving force command toprevent wheel slip. Furthermore, in the case of the rear wheel and wheelaxle, even when the natural frequency component of the vehiclesuspension pitch motion is enhanced in the driving force command, wheelslip rarely occurs. Thus, it is desirable to control the brakingperformance by enhancing the natural frequency component with respect tothe driving force command.

This is reversed while the vehicle is decelerating (regenerativebraking). While the vehicle is decelerating, pitch motion occurs in anose-down (dive) direction and the load is shifted forward thereof.Therefore, when compared to a neutral load state (stationary state), thevertical load on the front axle increases, making it difficult to causeslip, and the vertical load on the rear axle decreases, making it easyto generate slip.

Therefore, in the present instance, in the rear wheel and the rear axle,it is desirable to perform a control operation to prevent wheel lock byremoving a natural frequency component of the pitch motion from theregenerative braking force command. In the front wheel and the frontaxle, wheel lock hardly occurs even when the natural frequency componentof the pitch motion is enhanced in the regenerative braking forcecommand, and thus it is desirable to perform a control operation toenhance the braking performance and increase the amount of regenerationby enhancing the natural frequency component.

In consideration of the present point, in an exemplary embodiment of thepresent disclosure, a filter that removes the natural frequencycomponent of the vehicle suspension pitch motion (natural frequencyremoval filter) or a filter that enhances the natural frequencycomponent (natural frequency enhancement filter) is applied to theregenerative braking force command for each of the front axle and therear axle, so that control may be implemented, preventing wheel slip andmaximizing braking performance.

At the present time, to set drivability and driving performance, it ispossible to perform a control operation of selectively applying filtersto both axles, or compensating for a torque difference between the frontand rear wheels caused by an effect of applying a filter on one axle tothe other axle.

To remove or enhance the frequency component that excites the suspensionpitch motion of the vehicle in the regenerative braking force commandusing the filter, first, the frequency characteristic of the suspensionpitch motion for the vehicle to be controlled needs to be identified.This process may be performed by constructing various types of transferfunctions.

In an exemplary embodiment of the present disclosure, for regenerativebraking control, information of a transfer function is used, in which avariable representing a vehicle driving state is taken as input andstate information related to suspension pitch motion of the vehicle istaken as output. Here, the information of the transfer function may be anatural frequency, and the state information related to the suspensionpitch motion, which is output of the transfer function, may besuspension pitch angle information or tire vertical load information.

Here, the tire vertical load information may include a front wheelvertical load and a rear wheel vertical load. In the followingdescription, “front wheel vertical load” may be replaced with “frontaxle vertical load”, and “rear wheel vertical load” may be replaced with“rear axle vertical load”.

In an exemplary embodiment of the present disclosure, the suspensionpitch angle (hereinafter abbreviated as “pitch angle”) or the tirevertical load (hereinafter abbreviated as “vertical load”) may bedetermined using a transfer function, and an example of determining thepitch angle or vertical load using the transfer function will bedescribed as follows.

In an exemplary embodiment of the present disclosure, the transferfunction is modeled and constructed to be able to determine stateinformation related to the suspension pitch motion of the vehicle byinputting a variable representing the vehicle driving state. Here, thestate information related to the suspension pitch motion of the vehiclemay be a pitch angle or a vertical load.

FIG. 4 is a diagram illustrating that a pitch angle or a vertical loadmay be determined using a transfer function, which takes a variablerepresenting a vehicle driving state as input thereof, in an exemplaryembodiment of the present disclosure. In various exemplary embodimentsof the present disclosure, the transfer function may take the followingform.

First, a transfer function taking regenerative braking force informationas input and taking pitch angle information as output, or a transferfunction taking pitch angle information as input and taking verticalload information as output may be constructed in the control unit (firstcontrol unit 20) and used. Here, the regenerative braking forceinformation may be a required regenerative braking force command(required regenerative braking torque command) determined by the controlunit.

The required regenerative braking force command and the pitch angle,which are input to the transfer function, are variable informationindicating the vehicle driving state, and may be obtained frominformation detected by the sensor 10. It has been described above thatthe required regenerative braking force command is determined from thesensor detection information, and that the pitch angle may be obtainedfrom information detected by a suspension device position sensor.

Alternatively, a transfer function taking regenerative braking forceinformation as input and taking vertical load information as output, ora transfer function taking tire pressure information detected by a tirepressure sensor as input and taking vertical load information as outputmay be constructed in the control unit and used.

Alternatively, a transfer function taking longitudinal or verticalacceleration information of the vehicle detected by a longitudinalacceleration sensor or a vertical acceleration sensor provided in thevehicle as input and taking pitch angle or vertical load information asoutput may be constructed in the control unit and used.

Alternatively, a transfer function taking pitch angle change rate (pitchrate) information obtained by a gyro sensor (pitch rate sensor) as inputand taking pitch angle or vertical load information as output may beconstructed in the control unit and used.

Alternatively, a transfer function taking a drive system speed as inputand taking pitch angle or vertical load information as output may beconstructed in the control unit and used. Here, the drive system speedmay be a wheel speed, or a driving device speed (motor speed), ordriveshaft speed.

Alternatively, a transfer function taking information detected by asuspension travel sensor as input and taking pitch angle or verticalload information as output may be constructed in the control unit andused.

Alternatively, a transfer function taking two pieces or more of theabove-mentioned input information as input and taking pitch angle orvertical load information as output may be constructed in the controlunit and used.

Here, the transfer function may be set to determine the pitch angle orvertical load using a data-based optimization technique or a numericalsolution.

Alternatively, a transfer function based on a physical model may beconstructed and used, or a learning technique may be used to obtain thetransfer function. Furthermore, an algorithm including the above inputand output may be constructed using various machine learning techniquesin addition to the transfer function.

Meanwhile, a state in which the transfer function is constructed in thecontrol unit, that is, in a state in which a transfer function capableof outputting pitch angle or vertical load information, which is stateinformation related to the suspension pitch motion of the vehicle, bytaking a variable representing the vehicle driving state as input isconstructed, a natural frequency of the transfer function may bedetermined. In the present instance, the transfer function may representthe unique characteristics of the vehicle to which the regenerativebraking control method of the present disclosure is applied.

In an exemplary embodiment of the present disclosure, as describedabove, the natural frequency of the transfer function constructed tooutput the state information related to the suspension pitch motion ofthe vehicle by taking the variable representing the vehicle drivingstate as input may be regarded as a natural frequency of suspensionpitch motion vibration in a vehicle to be controlled. In the followingdescription, “the natural frequency of the transfer function” and “thenatural frequency of the vehicle suspension pitch motion” may have thesame meaning.

Furthermore, in a state in which the natural frequency of the vehiclesuspension pitch motion, that is, the natural frequency of thepre-constructed transfer function is determined as described above, afilter to be applied to the regenerative braking force command isconfigured and set in the control unit based on natural frequencyinformation of the determined transfer function to control regenerativebraking of the vehicle.

In the instant case, a filter capable of removing a frequency componentcorresponding to the natural frequency of the transfer function from theregenerative braking force command may be configured and set in thecontrol unit. In various exemplary embodiments of the presentdisclosure, the filter may be a filter configured and set using aLaplace transfer function.

As described above, in a state in which the transfer function isconstructed in the control unit of the vehicle to which an exemplaryembodiment of the present disclosure is actually applied, suspensionpitch motion information of the vehicle (state information related tothe suspension pitch motion of the vehicle), such as a pitch angle orvertical load, which is the output of the transfer function, may be usedin various ways for vehicle control. Furthermore, the natural frequencyof the transfer function constructed in the control unit of the vehiclemay be used to design and configure the filter in the control unit as inan exemplary embodiment of the present disclosure.

Furthermore, as described above, the natural frequency is not determinedin a state in which the transfer function is constructed in the controlunit of the actual vehicle to which an exemplary embodiment of thepresent disclosure is applied, and the natural frequency of the transferfunction may be obtained after the transfer function described above isconstructed through a preceding evaluation and test process conducted ina development stage of the same type of vehicle. Furthermore, a filterdesigned using the natural frequency information obtained in the instantway may be configured and set in a control unit of an actualmass-produced vehicle and used for regenerative braking control.

Hereinafter, an example of filter application will be described in moredetail.

In the following description, “regenerative braking force command” mayrefer to one of a required regenerative braking force command determinedbased on vehicle driving information in the first control unit 20, afront wheel regenerative braking force command, which is a commandgenerated to apply a regenerative braking force distributed to the frontwheel based on the required regenerative braking force command, and arear wheel regenerative braking force command, which is a commandgenerated to apply a regenerative braking force distributed to the rearwheel based on the required regenerative braking force command. That is,the “regenerative braking force command” may be understood to encompassall of the required regenerative braking force command, the front wheelregenerative braking force command, and the rear wheel regenerativebraking force command.

In the following description, “front wheel regenerative braking forcecommand” may be a torque command for the front wheel and the front axle,which may be a regenerative braking torque command of the front wheeldriving device (for example, a regenerative braking torque command of afront wheel motor). That is, “front wheel regenerative braking forcecommand” may be a command of a torque value applied to the front wheeland the front axle by the front wheel driving device.

Furthermore, in the following description, “rear wheel regenerativebraking force command” may be a torque command for the rear wheel andthe rear axle, which may be a regenerative braking torque command of therear wheel driving device (a regenerative braking torque command of arear wheel motor). That is, “rear wheel regenerative braking forcecommand” may be a command of a regenerative braking torque value appliedto the rear wheel and the rear axle by the rear wheel driving device.

FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, FIG. 5F, FIG. 5G, and FIG.5H are diagrams for describing various examples in which a final frontwheel regenerative braking force command and a final rear wheelregenerative braking force command are obtained using a filterconfigured for removing the natural frequency component of the transferfunction in an exemplary embodiment of the present disclosure, andillustrate examples of using the filter configured for removing thenatural frequency component of the transfer function, that is, a filterconfigured for removing the natural frequency component of the vehiclesuspension pitch motion from the regenerative braking force command.

In FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, FIG. 5F, FIG. 5G, andFIG. 5H, a vertical axis represents regenerative braking force and ahorizontal axis represents time. Furthermore, unlike the driving forcewhich may be expressed as a positive (+) value, the regenerative brakingforce may be expressed as a negative (−) value, as may be seen from thedrawings.

Furthermore, the driving torque is torque in a forward direction foraccelerating the vehicle, and is generally expressed as positive (+)torque among those skilled in the art. Furthermore, the regenerativebraking torque is torque in a reverse direction for decelerating thevehicle, and is generally expressed as negative (−) torque among thoseskilled in the art. This is equally applied in an exemplary embodimentof the present disclosure.

First, as illustrated in FIG. 5A, a control operation may be performedby applying a filter configured to be able to remove the naturalfrequency component of the transfer function (that is, the naturalfrequency component of the vehicle suspension pitch motion) from theregenerative braking force command only to the rear wheel regenerativebraking force command. After the filter is applied, the rear wheelregenerative braking force command becomes the final rear wheelregenerative braking force command, and the front wheel regenerativebraking force command to which the filter is not applied (before thefilter is applied) becomes the final front wheel regenerative brakingforce command.

As an exemplary embodiment of the present disclosure, as illustrated inFIG. 5B, the front wheel regenerative braking force command may becorrected by applying the filter only to the rear wheel regenerativebraking force command, and compensating for a difference between therear wheel regenerative braking force command before application of thefilter and the rear wheel regenerative braking force command afterapplication of the filter (that is, a difference in the regenerativebraking force command due to the filter) in the front wheel regenerativebraking force command to which the filter is not applied. In the presentinstance, compensation may be performed so that the difference betweenthe rear wheel regenerative braking force command before application ofthe filter and the rear wheel regenerative braking force command afterapplication of the filter is added to the front wheel regenerativebraking force command to which the filter is not applied.

As a result, both the front wheel regenerative braking force command andthe rear wheel regenerative braking force command are corrected by thefilter, the rear wheel regenerative braking force command is determinedas a value to which the filter is applied, and the front wheelregenerative braking force command is determined as a value obtained bycompensating for the difference between the rear wheel regenerativebraking force commands before and after application of the filter.

In the example of FIG. 5B, the rear wheel regenerative braking forcecommand after the filter is applied becomes the final rear wheelregenerative braking force command, and the front wheel regenerativebraking force command after compensation becomes the final front wheelregenerative braking force command. In the present instance, both thefront wheel regenerative braking force command after the filter isapplied and the rear wheel regenerative braking force command aftercompensation may be referred to as regenerative braking force commandscorrected using the filter.

As an exemplary embodiment of the present disclosure, as illustrated inFIG. 5C, it is possible to perform a control operation by applying thefilter to the required regenerative braking force command, which is theregenerative braking force command before distribution to the front andrear wheels. At the instant time, after the filter is applied to therequired regenerative braking force command, the required regenerativebraking force command after application of the filter is distributed tothe front and rear wheels according to the front and rear wheel powerdistribution ratio (hereinafter abbreviated as “power distributionratio”), so that the front wheel regenerative braking force command andthe rear wheel regenerative braking force command are determined.

The required regenerative braking force command is a normal regenerativebraking force command (regenerative braking torque command) determinedby the control unit based on vehicle driving information, is aregenerative braking force command before power distribution to thefront and rear wheels, and is a regenerative braking force commandbefore the filter is applied.

In the present way, the filter may be applied to the requiredregenerative braking force command, and after the filter is applied tothe required regenerative braking force command, the requiredregenerative braking force command after application of the filter isdistributed according to the power distribution ratio, so that the finalfront wheel regenerative braking force command and the final rear wheelregenerative braking force command may be determined.

As an exemplary embodiment of the present disclosure, as illustrated inFIG. 5D, the distributed front wheel regenerative braking force commandmay be corrected using a difference in the regenerative braking forcecommand due to the filter, that is, a difference between the requiredregenerative braking force command before application of the filter andthe required regenerative braking force command after application of thefilter. Here, the distributed front wheel regenerative braking forcecommand is a front wheel regenerative braking force command distributedfrom the required regenerative braking force command after applicationof the filter.

That is, the front wheel regenerative braking force command may becorrected so that the distributed front wheel regenerative braking forcecommand is compensated by the difference between the requiredregenerative braking force commands before and after application of thefilter, and the front wheel regenerative braking force command aftercompensation may be used as the final front wheel regenerative brakingforce command in controlling the regenerative braking of the vehicle.

In the present instance, compensation may be performed by adding thedifference between the required regenerative braking force commandsbefore and after application of the filter to the distributed frontwheel regenerative braking force command. Furthermore, the rear wheelregenerative braking force command distributed from the requiredregenerative braking force command after application of the filter isused as the final rear wheel regenerative braking force command.

As an exemplary embodiment of the present disclosure, as illustrated inFIG. 5E, after applying the filter to the required regenerative brakingforce command, each of the required regenerative braking force commandafter the filter is applied and the required regenerative braking forcecommand before the filter is applied is distributed according to thepower distribution ratio, and the rear wheel regenerative braking forcecommand distributed from the required regenerative braking force commandafter the filter is applied and the front wheel regenerative brakingforce command distributed from the required regenerative braking forcecommand before the filter is applied may be used as the final frontwheel regenerative braking force command and the final rear wheelregenerative braking force command, respectively.

As an exemplary embodiment of the present disclosure, as illustrated inFIG. 5F, after performing correction for compensating each of the frontwheel regenerative braking force command and the rear wheel regenerativebraking force command distributed from the required regenerative brakingforce command before application of the filter by a difference betweenthe required regenerative braking force command before application ofthe filter and the required regenerative braking force command afterapplication of the filter (difference in the regenerative braking forcecommand due to the filter), the front wheel regenerative braking forcecommand after compensation and the rear wheel regenerative braking forcecommand after compensation may be used to control the regenerativebraking of the vehicle.

In the present instance, the difference between the requiredregenerative braking force command before application of the filter andthe required regenerative braking force command after application of thefilter (difference in the regenerative braking force command due to thefilter) may be subtracted from the rear wheel regenerative braking forcecommand distributed from the required regenerative braking force commandbefore application of the filter, and the rear wheel regenerativebraking force command after subtraction (that is, after compensation)may be used to control the regenerative braking of the vehicle.

Furthermore, after adding the difference between the requiredregenerative braking force command before application of the filter andthe required regenerative braking force command after application of thefilter (difference in the regenerative braking force command due to thefilter) to the front wheel regenerative braking force commanddistributed from the required regenerative braking force command beforeapplication of the filter, the front wheel regenerative braking forcecommand after addition (that is, after compensation) may be used tocontrol the regenerative braking of the vehicle.

Furthermore, as in the example of FIG. 5F, when correction is performedto compensate the regenerative braking force command by the differencebetween the command before application of the filter and the commandafter application of the filter (difference in the regenerative brakingforce command due to the filter), a value of the compensatedregenerative braking force command (after compensation) may be preventedfrom becoming smaller or greater than a preset limit value (upper limitand lower limit). That is, the value of the compensated regenerativebraking force command (after compensation) is limited so that the valuedoes not become greater than the upper limit, or the value of thecompensated regenerative braking force command is limited so that thevalue does not become smaller than the lower limit.

Here, in determining the difference in the regenerative braking forcecommand due to the filter, the command before application of the filtermay be the required regenerative braking force command beforeapplication of the filter (see the examples of FIGS. 5D and 5F) or therear wheel regenerative braking force command before application of thefilter (see the example of FIG. 5B). Similarly, the command afterapplication of the filter may be the required regenerative braking forcecommand after application of the filter (see the examples of FIGS. 5Dand 5F) or the rear wheel regenerative braking force command afterapplication of the filter (see the example of FIG. 5B).

Furthermore, in limiting the value of the regenerative braking forcecommand after compensation by the difference, that is, the value of thecompensated regenerative braking force command, the regenerative brakingforce command before application of the filter, or a value obtained bymultiplying a scale value of 1 or more by the regenerative braking forcecommand before application of the filter may be set and used as a lowerlimit of the corrected regenerative braking force command. Furthermore,0 or the regenerative braking force command before application of thefilter or a value obtained by multiplying a scale value between 0 and 1by the regenerative braking force command before application of thefilter may be set and used as an upper limit of the correctedregenerative braking force command (see FIG. 5G).

Here, the corrected regenerative braking force command may be the frontwheel regenerative braking force command after compensation and the rearwheel regenerative braking force command after compensation compensatedby the difference in the regenerative braking force command due to thefilter, and the regenerative braking force command before application ofthe filter used to set the upper limit and the lower limit may be thefront wheel regenerative braking force command and the rear wheelregenerative braking force command distributed from the requiredregenerative braking force command before application of the filter.

Referring to FIG. 5G, the upper limit is set to 0, and the lower limitis set to a value obtained by multiplying the regenerative braking forcecommand before application of the filter by a scale value of 1 or more(=2). Furthermore, the lower limit is applied to the corrected frontwheel regenerative braking force command (after compensation), and theupper limit is applied to the corrected rear wheel regenerative brakingforce command (after compensation).

The regenerative braking force command before application of the filterused to set the lower limit may be the front wheel regenerative brakingforce command distributed from the required regenerative braking forcecommand before application of the filter. In the example of FIG. 5G, theupper limit 0 is applied to the corrected rear wheel regenerativebraking force command (after compensation) in a state where 0 is set asthe upper limit in the control unit, and the rear wheel regenerativebraking force command to which the upper limit is applied in the instantway is used as the final rear wheel regenerative braking force commandto control the regenerative braking force of the vehicle.

Furthermore, in the example of FIG. 5G, a value obtained by multiplyingthe front wheel regenerative braking force command distributed from therequired regenerative braking force command before application of thefilter (that is, the existing command) by a predetermined scale value 2is set as the lower limit, the lower limit is applied to the correctedfront wheel regenerative braking force command (after compensation) in astate where the lower limit is set in the control unit, and the frontwheel regenerative braking force command to which the lower limit isapplied is used as the final front wheel regenerative braking forcecommand to control the regenerative braking force of the vehicle.

As described above, when a limit value for limiting the regenerativebraking force command of the wheel, that is, the upper limit and thelower limit are determined, the rear wheel regenerative braking forcecommand and the front wheel regenerative braking force commanddetermined by applying the upper limit and the lower limit may bedirectly used for controlling the regenerative braking of the vehicle.However, after modifying the regenerative braking force command of thewheel (front wheel or rear wheel), to which the limit value (upper limitor lower limit) is applied, to determine a modified regenerative brakingforce command of the wheel (to which the limit value is applied) througha subsequent additional process, the modified regenerative braking forcecommand of the wheel may be used to control the regenerative braking ofthe vehicle (see FIG. 5H).

Here, the modified regenerative braking force command of the wheel mayinclude a modified upper limit-applied rear wheel regenerative brakingforce command and a modified lower limit-applied front wheelregenerative braking force command.

In more detail, when the rear wheel regenerative braking force commandand the front wheel regenerative braking force command to which theupper or lower limit is applied are determined, a difference between therear wheel regenerative braking force command distributed from therequired regenerative braking force command before application of thefilter and the rear wheel regenerative braking force command to whichthe limit value is applied is determined as the amount of correction ofthe rear wheel. Here, the rear wheel regenerative braking force commandto which the limit value is applied may be the rear wheel regenerativebraking force command to which the upper limit is applied.

That is, when the upper limit is applied to the corrected rear wheelregenerative braking force command (after compensation) to determine therear wheel regenerative braking force command to which the upper limitis applied, a difference between the distributed rear wheel regenerativebraking force command and the rear wheel regenerative braking forcecommand to which the upper limit is applied is determined and determinedas the amount of correction of the rear wheel.

Similarly, a difference between the front wheel regenerative brakingforce command distributed from the required regenerative braking forcecommand before application of the filter and the front wheelregenerative braking force command to which the limit value is appliedis determined as the amount of correction of the front wheel. Here, thefront wheel regenerative braking force command to which the limit valueis applied may be the front wheel regenerative braking force command towhich the lower limit is applied.

That is, when the lower limit is applied to the corrected front wheelregenerative braking force command (after compensation) to determine thefront wheel regenerative braking force command to which the lower limitis applied, a difference between distributed the front wheelregenerative braking force command and the front wheel regenerativebraking force command to which the lower limit is applied is determinedand determined as the amount of correction of the front wheel.

Furthermore, when the amount of correction of the rear wheel and theamount of correction of the front wheel are determined as describedabove, the absolute value of the determined amount of correction of therear wheel is compared with the absolute value of the determined amountof correction of the front wheel, and a wheel having the small absolutevalue of the correction amount and a wheel having the large absolutevalue of the correction amount are determined.

Then, the correction amount on the wheel side including small absolutevalue of the correction amount (that is, the correction amount includinga relatively small absolute value) is determined and set as an upperlimit of the correction amount on the wheel side including a largeabsolute value of the correction amount. Furthermore, a value obtainedby multiplying the correction amount on the wheel side including a smallabsolute value of the correction amount (that is, the correction amountincluding a relatively small absolute value) by −1 is determined and setas a lower limit of the correction amount on the wheel side including alarge absolute value of the correction amount.

Subsequently, the correction amount on the wheel side including thelarge absolute value of the correction amount is limited to the upperlimit and the lower limit of the correction amount to modify thecorrection amount, the modified correction amount and the distributedregenerative braking force command of the corresponding wheel aresummed, and the sum value is determined as the modified regenerativebraking force command of the corresponding wheel, that is, the modified,limit value-applied regenerative braking force command of thecorresponding wheel. Furthermore, the modified regenerative brakingforce command of the corresponding wheel determined in the instant wayis used to control the regenerative braking of the vehicle.

In the present instance, in the case of a wheel including a smallabsolute value of the correction amount, the regenerative braking forcecommand (after compensation), which is corrected using the methoddescribed with reference to FIG. 5G, may be used to control theregenerative braking of the vehicle without change.

In summary, after comparing the absolute value of the correction amountof the front wheel with the absolute value of the correction amount ofthe rear wheel to determine a first wheel including a small absolutevalue of the correction amount and a second wheel including a largeabsolute value of the correction amount in the front wheel and the rearwheel, the correction amount on the first wheel side is determined as anupper limit of the correction amount on the second wheel side, and avalue obtained by multiplying the correction amount on the first wheelside by −1 is determined as a lower limit of the correction amount onthe second wheel side.

Accordingly, the regenerative braking force command on the second wheelside to which the upper limit or the lower limit is applied is modifiedbased on the determined upper limit of the correction amount on thesecond wheel side and the correction amount on the second wheel sidelimited to the lower limit of the correction amount on the second wheelside, and the modified regenerative braking force command on the secondwheel side is determined as the front wheel regenerative braking forcecommand or the rear wheel regenerative braking force command forcontrolling the regenerative braking.

In the example of FIG. 5G, the lower limit is applied to the correctedfront wheel regenerative braking force command, and the front wheelregenerative braking force command limited by the lower limit is used tocontrol the regenerative braking of the vehicle. Furthermore, the upperlimit is applied to the corrected rear wheel regenerative braking forcecommand, and the rear wheel regenerative braking force command limitedby the upper limit is used to control the regenerative braking of thevehicle.

Furthermore, in the example of FIG. 5H, the absolute value of thecorrection amount of the rear wheel is smaller than the absolute valueof the correction amount of the front wheel, and accordingly, thecorrection amount of the rear wheel is set as the upper limit of thecorrection amount of the front wheel. As described above, in the exampleof FIG. 5H, the rear wheel is the first wheel and the front wheel is thesecond wheel.

At the present time, a value obtained by multiplying the absolute valueof the correction amount of the rear wheel by −1 is set as the lowerlimit of the correction amount of the front wheel. As a result, thecorrection amount of the front wheel is limited by the correction amountof the rear wheel. In the illustrated example, all the absolute valuesof the correction amount of the front wheel are greater than theabsolute value of the correction amount of the rear wheel. In theinstant case, the correction amount of the front wheel becomes the sameas the correction amount of the rear wheel.

Accordingly, the modified lower limit-applied front wheel regenerativebraking force command may be determined by applying the modifiedcorrection amount of the front wheel. At the instant time, the frontwheel regenerative braking force command distributed from the requiredregenerative braking force command before application of the filter isadded to the modified correction amount of the front wheel, and thesummed value becomes the modified lower limit-applied front wheelregenerative braking force command.

Accordingly, the modified lower limit-applied front wheel regenerativebraking force command is used as the final front wheel regenerativebraking force command to control the regenerative braking force of thefront wheel in controlling the regenerative braking of the vehicle. Inthe present instance, the final rear wheel regenerative braking forcebecomes the rear wheel regenerative braking force command determined inthe example of FIG. 5G, that is, the rear wheel regenerative brakingforce to which the upper limit is applied.

Furthermore, the control unit may determine whether to apply the filterbased on real-time vehicle driving information. Furthermore, when thefilter is applied to the regenerative braking force command as describedabove in the control unit, it is possible to apply a weight determinedbased on current vehicle driving information.

That is, to set the vehicle drivability, it is necessary to apply thefilter only to a specific region of the vehicle driving state, and it isnecessary to change whether the filter intervenes and a weight of filterapplication according to the vehicle driving state. Accordingly, it ispossible to determine whether to apply the filter according to thevehicle driving state by a state variable map preset in the control unit(the first control unit 20), and a weight according to the vehicledriving state may be obtained and used by the state variable map.

In various exemplary embodiments of the present disclosure, informationindicating the vehicle driving state for determining whether to applythe filter and the weight of the filter application, that is, vehicledriving information, may include at least one of regenerative brakingtorque, a drive system speed, a vehicle speed, or a driver driving inputvalue.

Here, the regenerative braking torque may be a current regenerativebraking force command value or a regenerative braking force commandvalue of an immediately preceding control cycle. Alternatively, theregenerative braking torque may be an estimated regenerative brakingtorque value which may be generated when the current regenerativebraking force command is applied or when the regenerative braking forcecommand of the immediately preceding control cycle is used.

In the present instance, the current regenerative braking force commandor the regenerative braking force command of the immediately precedingcontrol cycle may be the required regenerative braking force commandbefore application of the filter or the required regenerative brakingforce command after application of the filter. Furthermore, the drivesystem speed, the vehicle speed, and the driver driving input value maybe sensor detection information detected by the sensor 10, and thedriver driving input value may be a braking pedal input value (BPSvalue) of the driver.

In the control unit (the first control unit 20), the weight may bedetermined by the state variable map, and not only the weight but alsowhether to apply the filter may be determined by one state variable maptaking the vehicle driving information as input.

To the present end, a state variable map taking the vehicle drivinginformation as input and taking whether to apply the filter and weightinformation as output may be used while being previously input andstored in the control unit. In the present instance, in the statevariable map, a filter application region and a filter non-applicationregion may be separately set based on the vehicle driving state.Furthermore, in the case of the filter application region, a weight maybe set as a value according to the vehicle driving state.

As an example of weight application, when a weight determined by thestate variable map is a, a sum value of a value obtained by multiplyingthe regenerative braking force command after application of the filterby a and a value obtained by multiplying the regenerative braking forcecommand before application of the filter by 1−α may be determined as acommand after application of the final filter.

Weights α and 1×α corresponding to the current vehicle driving state aredetermined using the state variable map from the vehicle drivinginformation, and the front wheel regenerative braking force command andthe rear wheel regenerative braking force command distributed from therequired regenerative braking force command according to the powerdistribution ratio are determined without a limit value applicationprocess using the limit value.

Subsequently, values obtained by applying the determined weights α and1×α to a final front wheel regenerative braking force command determinedwithout the limit value application process using the limit value and afinal front wheel regenerative braking force command obtained throughthe limit value application process using the limit value, respectively,are summed.

Furthermore, values obtained by applying the determined weights α and1×α to a final rear wheel regenerative braking force command determinedwithout the limit value application process using the limit value and afinal rear wheel regenerative braking force command obtained through thelimit value application process using the limit value, respectively, aresummed.

Finally, the front wheel regenerative braking force command and the rearwheel regenerative braking force command obtained by the summing aredetermined as the final front wheel regenerative braking force commandand the final rear wheel regenerative braking force command.

Alternatively, as another example of applying the weight, it is possibleto adjust the filter gain according to the weight, and in the presentinstance, the filter gain obtained by multiplying by the weight may beused. In the state variable map, a weight a may be set to 0 in thefilter non-application region.

The regenerative braking control process described above with referenceto FIG. 3 is summarized as follows.

As illustrated in FIG. 3 , the vehicle driving information is obtainedin real time while the vehicle is driven (step S1), and the requiredregenerative braking force command is determined based on the vehicledriving information obtained by the control unit (the first control unit20) (step S2).

Accordingly, the control unit (the first control unit 20) determineswhether the current vehicle driving state satisfies a condition forapplying the filter in the state variable map, that is, whether thecurrent vehicle driving state corresponds to the filter applicationregion (step S3).

Upon determining that the current vehicle driving state does notcorrespond to the filter application region (weight α=0), the controlunit is configured to determine the final front wheel regenerativebraking force command and the final rear wheel regenerative brakingforce command from the required regenerative braking force command towhich the filter is not applied (step S6), and then is configured tocontrol the regenerative braking force of the vehicle according to thedetermined final front wheel regenerative braking force command and thedetermined final rear wheel regenerative braking force command (stepS7).

On the other hand, upon determining that the current vehicle drivingstate corresponds to the filter application region, the control unit isconfigured to apply the filter to the regenerative braking force command(for example, the front wheel regenerative braking force command) (stepS4), then determines a difference in the regenerative braking forcecommand due to the filter, and then performs correction for compensatingthe regenerative braking force command (for example, the rear wheelregenerative braking force command) by the difference (step S5).Subsequently, the determined front wheel regenerative braking forcecommand and rear wheel regenerative braking force command are determinedas the final front wheel regenerative braking force command and thefinal rear wheel regenerative braking force command, respectively (stepS6).

Furthermore, the regenerative braking force of the vehicle is controlledaccording to the determined final front wheel regenerative braking forcecommand and the determined final rear wheel regenerative braking forcecommand (step S7). In determining the final front wheel regenerativebraking force command and the final rear wheel regenerative brakingforce command, it is possible to apply a weight determined by the statevariable map as described above.

Next, as another exemplary embodiment of the present disclosure, insteadof the filter configured to remove the natural frequency component ofthe transfer function (that is, the natural frequency removal filter), afilter configured to be able to pass the natural frequency component ofthe transfer function may be set in the control unit and used.

Here, passing the natural frequency component has the meaning ofenhancing the natural frequency component in the regenerative brakingforce command. Accordingly, in an exemplary embodiment of the presentdisclosure, the filter that passes the natural frequency component (thatis, a natural frequency pass filter) may refer to a filter that enhancesthe natural frequency component (that is, the natural frequencyenhancement filter).

FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E and FIG. 6F are diagrams fordescribing various examples in which a final front wheel regenerativebraking force command and a final rear wheel regenerative braking forcecommand are obtained using a filter that passes the natural frequencycomponent of the transfer function in an exemplary embodiment of thepresent disclosure, and illustrate examples using the filter configuredfor enhancing the natural frequency component of the vehicle suspensionpitch motion in the regenerative braking force command. In FIG. 6A, FIG.6B, FIG. 6C, FIG. 6D, FIG. 6E and FIG. 6F, a vertical axis representsregenerative braking force and a horizontal axis represents time.

In an exemplary embodiment using the filter that passes the naturalfrequency component of the transfer function, it is possible to use amethod of applying the filter to the regenerative braking force command,and then adding the regenerative braking force command after applicationof the filter to the regenerative braking force command beforeapplication of the filter or subtracting the regenerative braking forcecommand after application of the filter from the regenerative brakingforce command before application of the filter.

The exemplary embodiment using the natural frequency pass(reinforcement) filter will be described in more detail. First, thefilter that passes the natural frequency component may be applied onlyto the front wheel regenerative braking force command distributedaccording to the power distribution ratio as illustrated in FIG. 6A andFIG. 6B.

That is, when the required regenerative braking force command isdistributed according to the power distribution ratio and the frontwheel regenerative braking force command and the rear wheel regenerativebraking force command are determined, the filter is applied only to thefront wheel regenerative braking force command in the distributed frontwheel regenerative braking force command and rear wheel regenerativebraking force command.

Accordingly, as illustrated in FIG. 6A, the front wheel regenerativebraking force command after application of the filter may be added tothe front wheel regenerative braking force command before application ofthe filter, and the front wheel regenerative braking force command afteraddition may be used as the final front wheel regenerative braking forcecommand to control the regenerative braking of the vehicle.

In the present instance, as the final rear wheel regenerative brakingforce command, it is possible to use the rear wheel regenerative brakingforce command distributed according to the power distribution ratiowithout change. That is, the rear wheel regenerative braking forcecommand to which the filter is not applied after being distributed maybe used to control the regenerative braking of the vehicle withoutchange.

Alternatively, the required regenerative braking force command isdistributed according to the power distribution ratio to determine thefront wheel regenerative braking force command and the rear wheelregenerative braking force command, the filter is applied only to thefront wheel regenerative braking force command in the distributed frontwheel regenerative braking force command and rear wheel regenerativebraking force command, and then the front wheel regenerative brakingforce command after application of the filter is subtracted from therear wheel regenerative braking force command to which the filter is notapplied (that is, before application of the filter) as illustrated inFIG. 6B.

In the present way, the front wheel regenerative braking force commandafter application of the filter may be subtracted from the rear wheelregenerative braking force command to which the filter is not applied(that is, before application of the filter), and the rear wheelregenerative braking force command after subtraction may be used as thefinal rear wheel regenerative braking force command to control theregenerative braking control of the vehicle. At the instant time, thefront wheel regenerative braking force command after application of thefilter may be used as the final front wheel regenerative braking forcecommand to control the regenerative braking control of the vehicle.

Alternatively, the filter that passes the natural frequency componentmay be applied only to the rear wheel regenerative braking force commanddistributed according to the power distribution ratio as illustrated inFIGS. 6C and 6D.

That is, when the required regenerative braking force command isdistributed according to the power distribution ratio, and the frontwheel regenerative braking force command and the rear wheel regenerativebraking force command are determined, the filter is applied only to therear wheel regenerative braking force command in the distributed frontwheel regenerative braking force command and rear wheel regenerativebraking force command.

Accordingly, as illustrated in FIG. 6C, the rear wheel regenerativebraking force command after application of the filter may be added tothe front wheel regenerative braking force command to which the filteris not applied (that is, before application of the filter), and thefront wheel regenerative braking force command after addition may beused as the final front wheel regenerative braking force command tocontrol the regenerative braking of the vehicle.

In the present instance, the rear wheel regenerative braking forcecommand after application of the filter may be used as the final rearwheel regenerative braking force command to control the regenerativebraking of the vehicle.

Alternatively, the required regenerative braking force command isdistributed according to the power distribution ratio to determine thefront wheel regenerative braking force command and the rear wheelregenerative braking force command, the filter is applied only to therear wheel regenerative braking force command in the distributed frontwheel regenerative braking force command and rear wheel regenerativebraking force command, and then the rear wheel regenerative brakingforce command after application of the filter is subtracted from therear wheel regenerative braking force command before application of thefilter as illustrated in FIG. 6D.

In the present instance, the rear wheel regenerative braking forcecommand after application of the filter may be subtracted from the rearwheel regenerative braking force command before application of thefilter, and the rear wheel regenerative braking force command aftersubtraction may be used as the final rear wheel regenerative brakingforce command to control the regenerative braking of the vehicle.

Furthermore, as the final front wheel regenerative braking forcecommand, it is possible to use the front wheel regenerative brakingforce command distributed according to the power distribution ratiowithout change. That is, the front wheel regenerative braking forcecommand to which the filter is not applied before distribution may beused to control the regenerative braking of the vehicle without change.

Furthermore, the filter that passes the natural frequency component maybe applied to the required regenerative braking force command.

In the present instance, after applying the filter to the requiredregenerative braking force command, the required regenerative brakingforce command obtained by applying the filter, that is, the requiredregenerative braking force command after application of the filter, maybe added to the required regenerative braking force command beforeapplication of the filter, and the sum value may be determined as therequired regenerative braking force command. Alternatively, the requiredregenerative braking force command after application of the filter maybe subtracted from the required regenerative braking force commandbefore application of the filter, and the subtracted value may bedetermined as the required regenerative braking force command.

Accordingly, the required regenerative braking force command determinedin the instant way may be distributed according to the powerdistribution ratio to determine the front wheel regenerative brakingforce command and the rear wheel regenerative braking force command, andthe determined front wheel regenerative braking force command and rearwheel regenerative braking force command may be used as a finalregenerative braking force command to control the regenerative brakingof the vehicle.

Alternatively, as illustrated in FIG. 6E, the filter is applied to therequired regenerative braking force command, and the requiredregenerative braking force command to which the filter is not applied(that is, before application of the filter) is distributed according tothe power distribution ratio to determine the front wheel regenerativebraking force command and the rear wheel regenerative braking forcecommand.

Accordingly, the distributed front wheel regenerative braking powercommand is added to the required regenerative braking power commandafter application of the filter, and the front wheel regenerativebraking power command after addition is used as the final front wheelregenerative braking power command to control the regenerative brakingof the vehicle.

Similarly, the required regenerative braking force command afterapplication of the filter is subtracted from the distributed rear wheelregenerative braking force command, and the rear wheel regenerativebraking power command after subtraction is used as the final rear wheelregenerative braking power command to control the regenerative brakingof the vehicle.

Alternatively, as illustrated in FIG. 6F, the filter is applied to therequired regenerative braking force command, and the requiredregenerative braking force command to which the filter is not applied(that is, before application of the filter) is distributed according tothe power distribution ratio of the front wheel and the rear wheel todetermine the front wheel regenerative braking force command and therear wheel regenerative braking power command.

Subsequently, the required regenerative braking force command to whichthe filter is applied, that is, the required regenerative braking forcecommand after application of the filter, is distributed according to thepower distribution ratio of the front wheel and the rear wheel todetermine a front wheel distribution component and a rear wheeldistribution component. Here, the front wheel distribution componentafter application of the filter is a regenerative braking force commandpart distributed to the front wheel side in the required regenerativebraking force command after application of the filter, and the rearwheel distribution component after application of the filter is aremaining regenerative braking force command part distributed to therear wheel side in the required regenerative braking force command afterapplication of the filter.

Subsequently, the front wheel regenerative braking force commanddistributed from the required regenerative braking force command beforeapplication of the filter is added to the front wheel distributioncomponent after application of the filter, and the front wheelregenerative braking force command after addition is used as the finalfront wheel regenerative braking force command to control theregenerative braking of the vehicle.

Similarly, the rear wheel distribution component after application ofthe filter is subtracted the rear wheel regenerative braking forcecommand distributed from the required regenerative braking force commandbefore application of the filter, and the rear wheel regenerativebraking force command after subtraction is used as the final rear wheelregenerative braking force command to control the regenerative brakingof the vehicle.

Furthermore, in the case of applying the natural frequency pass filter,as in the case of applying the natural frequency removal filter, valuesof the front wheel regenerative braking force command after addition andthe rear wheel regenerative braking force command after subtraction maybe prevented from becoming smaller or greater than a preset limit value(upper limit or lower limit). That is, the value of the front wheelregenerative braking force command after addition or the rear wheelregenerative braking force command after subtraction is limited so thatthe value does not become greater than the upper limit or does notbecome smaller than the lower limit.

In limiting the values of the front wheel regenerative braking forcecommand after addition and the rear wheel regenerative braking forcecommand after subtraction, the regenerative braking force command beforeapplication of the filter or a value obtained by multiplying a scalevalue of 1 or more by the regenerative braking force command beforeapplication of the filter may be set as a lower limit of the front wheelregenerative braking force command after addition or the rear wheelregenerative braking force command after subtraction and used.

Furthermore, 0 or the regenerative braking force command beforeapplication of the filter or a value obtained by multiplying a scalevalue between 0 and 1 by the regenerative braking force command beforeapplication of the filter may be set as an upper limit of the frontwheel regenerative braking force command after addition or the rearwheel regenerative braking force command after subtraction and used.Here, the regenerative braking force command before application of thefilter may be the front wheel regenerative braking force command and therear wheel regenerative braking force command distributed from therequired regenerative braking force command before application of thefilter.

As a result, the final front wheel regenerative braking force command orrear wheel regenerative braking force command obtained in the examplesof FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E and FIG. 6F, for example,the front wheel regenerative braking force command after addition or therear wheel regenerative braking force command after subtraction in theexample of FIG. 6F may be limited so that the command does not becomegreater than the upper limit or does not become smaller than the lowerlimit, and limited values may be obtained as the final front wheelregenerative braking force command and the final rear wheel regenerativebraking force command and used to control the regenerative braking ofthe vehicle.

In the present instance, the lower limit may be applied to the frontwheel regenerative braking force command after addition, and the upperlimit may be applied to the rear wheel regenerative braking forcecommand after subtraction.

In addition to applying these upper and lower limits, as described withreference to FIG. 5H, after determining the regenerative braking forcecommand of the wheel to which the modified limit value is appliedthrough a subsequent additional process, the regenerative braking forcecommand of the wheel to which the modified limit value is applied may beused to control the regenerative braking of the vehicle.

Here, the regenerative braking force command of the wheel to which themodified limit value is applied may include a rear wheel regenerativebraking force command to which a modified upper limit is applied and afront wheel regenerative braking force command to which a modified lowerlimit is applied.

In more detail, when the rear wheel regenerative braking force commandand the front wheel regenerative braking force command to which theupper and lower limits are applied are determined, a difference betweenthe rear wheel regenerative braking force command distributed from therequired regenerative braking force command before application of thefilter and the rear wheel regenerative braking force command to whichthe limit value is applied is determined as the rear wheel correctionamount. Here, the rear wheel regenerative braking force command to whichthe limit value is applied may be the rear wheel regenerative brakingforce command to which the upper limit is applied.

That is, when the upper limit is applied to the rear wheel regenerativebraking force command after subtraction to determine the rear wheelregenerative braking force command to which the upper limit is applied,a difference between the distributed rear wheel regenerative brakingforce command and the rear wheel regenerative braking force command towhich the upper limit is applied is determined and determined as therear wheel correction amount.

Similarly, a difference between the front wheel regenerative brakingforce command distributed from the required regenerative braking forcecommand before application of the filter and the front wheelregenerative braking force command to which the limit value is appliedis determined as the front wheel correction amount. Here, the frontwheel regenerative braking force command to which the limit value isapplied may be the front wheel regenerative braking force command towhich the lower limit is applied.

That is, when the lower limit is applied to the front wheel regenerativebraking force command after addition to determine the front wheelregenerative braking force command to which the lower limit is applied,a difference between the distributed front wheel regenerative brakingforce command and the front wheel regenerative braking force command towhich the lower limit is applied is determined and determined as thefront wheel correction amount.

Accordingly, when the rear wheel correction amount and the front wheelcorrection amount are determined as described above, the absolute valueof the determined rear wheel correction amount and the absolute value ofthe front wheel correction amount are compared with each other, and awheel including a small absolute value of the correction amount and awheel including a large absolute value of the correction amount aredetermined.

Subsequently, the correction amount on a wheel side including a smallabsolute value of the correction amount (that is, the correction amountincluding a relatively small absolute value) is determined and set as anupper limit of the correction amount on a wheel side including a largeabsolute value of the correction amount. Furthermore, a value obtainedby multiplying the correction amount on the wheel side including thesmall absolute value of the correction amount (that is, the correctionamount including the relatively small absolute value) by −1 isdetermined and set as a lower limit of the correction amount on thewheel side including the large absolute value of the correction amount.

Subsequently, the correction amount on the wheel side including thelarge absolute value of the correction amount is limited to the upperlimit of the correction amount and the lower limit of the correctionamount to modify the correction amount, the present modified correctionamount is added to the distributed regenerative braking force command ofthe corresponding wheel, and the added value is determined as theregenerative braking force command of the corresponding wheel to whichthe modified limit value is applied. Furthermore, the regenerativebraking force command of the corresponding wheel, to which the modifiedlimit value is applied, determined in the instant way is used to controlthe regenerative braking of the vehicle.

Furthermore, in the exemplary embodiment in which the filter for passingthe natural frequency component is used as described above, a method ofusing a weight is applied in the same way as in the exemplary embodimentusing the filter for removing the natural frequency component. The useof weights in an exemplary embodiment of the present disclosure is notdifferent from that in the exemplary embodiment in which the filter forremoving the natural frequency component is used, and thus a descriptionthereof will be omitted.

Furthermore, as various exemplary embodiments of the present disclosure,the control unit may intermittently shift a removal target naturalfrequency or a pass target natural frequency of the filter based onvehicle weight information in real time or at predetermined intervals.

Typically, the natural frequency of the suspension pitch motion does notchange unless a vehicle suspension structure or settings are changed.However, the natural frequency may be changed due to a change in vehicleweight.

For example, when a change in vehicle weight occurs by a large changeamount of 10% or more of the total weight of the vehicle, the naturalfrequency is changed, and thus a filter modeled based on information ofa pre-constructed transfer function may not be effective. Therefore, itis desirable to shift a value of the natural frequency removed andpassed through the filter according to the change in vehicle weight.

In an exemplary embodiment of the present disclosure, vehicle weightinformation may be estimated based on real-time information collectedthrough a sensor in the vehicle by the control unit. For example, toobtain vehicle weight information, it is possible to use a vehicleweight estimation method included in Korean Patent Application Laid-OpenNo. 10-2021-0068873 (Jun. 10, 2021) filed by the present inventor.

According to Patent Publication No. 10-2021-0068873 (US PatentApplication Publication No. 2021/0163018), noise is removed by filteringan acceleration signal input from an acceleration sensor in a vehicle ata moment of stopping, a cycle value of the acceleration signal isdetermined from the noise-free acceleration signal, and then a vehicleweight may be estimated in real time using information of the determinedcycle value.

Hereinafter, a more detailed description will be provided of aconfiguration of a filter configured for removing a specific frequencycomponent (natural frequency component) of the pre-constructed transferfunction.

As described above, the transfer function is constructed to determinethe state information related to the suspension pitch motion of thevehicle by taking a variable representing the vehicle driving state asinput. Here, the state information related to the suspension pitchmotion of the vehicle may be a pitch angle or vertical load.

In an exemplary embodiment of the present disclosure, as a specificfrequency component of the transfer function, a frequency component tobe removed through the filter may be a natural frequency component ofthe vehicle suspension pitch motion, and a regenerative braking forcecommand including a frequency component corresponding to the naturalfrequency of the vehicle suspension pitch motion excites the vehiclesuspension pitch motion.

Therefore, the frequency to be removed through the filter may bedetermined as the natural frequency of the vehicle suspension pitchmotion and be used to configure the filter. In the present instance, thenatural frequency of the vehicle suspension pitch motion may bedetermined as the natural frequency of a transfer function taking thepitch angle or vertical load, which is state information related to thesuspension pitch motion, as output as described above.

In an exemplary embodiment of the present disclosure, when the vehiclesuspension pitch motion vibration is analyzed in the frequency domain(for example, analyzed in a Bode plot), a primary frequency, at whichthe peak gain occurs, may be defined as the natural frequency.

A regenerative braking force command including a frequency componentcorresponding to the above-mentioned natural frequency excites thevehicle suspension pitch motion, and as a result, longitudinal loadmovement severely occurs. Thus, a possibility that slip will occurincreases in one of the front wheel and the rear wheel having tractiondecreased due to the longitudinal load movement. Therefore, it isdesirable to remove the natural frequency component from theregenerative braking force command to reduce the wheel slip of thevehicle and decrease the suspension pitch motion.

Accordingly, in an exemplary embodiment of the present disclosure,information related to a transfer function that takes the stateinformation related to the suspension pitch motion of the vehicle asoutput is used. A filter configured for removing the natural frequencycomponent of the transfer function using the natural frequencyinformation of the transfer function indicating the natural frequency ofthe vehicle suspension pitch motion is configured in the control unit(first control unit 20). The control unit utilizes the filter to correctthe regenerative braking force command.

At the present time, the filter may be a low-pass filter including acut-off frequency corresponding to the natural frequency of the transferfunction of the suspension pitch motion, a notch filter (a band stopfilter or a band cancellation filter) including a center frequencycorresponding to the natural frequency, etc.

In an exemplary embodiment of the present disclosure, because the filteris used to remove, from the regenerative braking force command, acomponent corresponding to the natural frequency of the transferfunction of the pre-constructed suspension pitch motion as describedabove, the cut-off frequency of the low-pass filter or the centerfrequency of the notch filter may not match a natural frequency to beremoved.

However, considering an error range of a set natural frequency value,the natural frequency to be removed needs to be higher than the cut-offfrequency of the low-pass filter, and the natural frequency to beremoved needs to fall within a stop band of the notch filter.

In addition to the low-pass filter or the notch filter, amulti-dimensional filter may be used to remove the componentcorresponding to the natural frequency. Furthermore, the filter may bedesigned using the transfer function itself constructed by modeling thereal-time vertical load caused by the above-described suspension pitchmotion or longitudinal load movement of the vehicle.

For example, it is assumed that a transfer function TF for deriving apitch angle (squat angle, φ) from an actual regenerative braking forcecommand (torque command, Tq) is constructed as in the following Equation1.

$\begin{matrix}{{TF} = {\frac{\phi}{Tq} = \frac{1}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}} & \left\lbrack {{Equation}1} \right\rbrack\end{matrix}$

In the instant case, a filter based on the transfer function TF may bedesigned and configured as illustrated in Equation 2 below, and may beapplied to the regenerative braking force command by the control unitand used to control the regenerative braking of the vehicle.

$\begin{matrix}\begin{matrix}{{1 - {c_{4}s{TF}} - {c_{5}{TF}}} = {1 - \frac{c_{4}s}{{c_{1}s^{2}} + {c_{2}s} + c_{3}} - \frac{c_{5}}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}} \\{= {\frac{1}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}\left( {{c_{1}s^{2}} + {c_{2}s} + c_{3} - {c_{4}s} - c_{5}} \right)}} \\{= \frac{{c_{1}s^{2}} + {\left( {c_{2} - c_{4}} \right)s} + \left( {c_{3} - c_{5}} \right)}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}\end{matrix} & \left\lbrack {{Equation}2} \right\rbrack\end{matrix}$

Here, c₁, c₂, c₃, c₄, c₅, etc. are coefficients which may be set(positive or negative), and s is a Laplace operator.

Previously, it has been described that the natural frequency to beremoved or the natural frequency to be passed, which is applied to thefilter, may be shifted according to the change in vehicle weight. Avalue of the natural frequency may be shifted by changing the filterconfiguration, for example, by changing values of the Laplace operatorsc₁, c₂, c₃, c₄, and c₅ in the filter according to a shifted value.

Next, a more detailed description will be given of the configuration ofthe filter configured for passing the specific frequency component(natural frequency component) of the pre-constructed transfer function.

In an exemplary embodiment of the present disclosure, as the specificfrequency component of the transfer function, the frequency componentpassing through the filter may be the natural frequency component of thevehicle suspension pitch motion. As described above, the regenerativebraking force command including the frequency component corresponding tothe natural frequency of the vehicle suspension pitch motion excites thevehicle suspension pitch motion.

As a result, the longitudinal load movement of the vehicle severelyoccurs, and a possibility that slip will occur increases in one of thefront wheel and the rear wheel of the vehicle having traction decreaseddue to the longitudinal load movement.

However, on the other hand, an environment in which slipping hardlyoccurs is generated in one of the front wheel and the rear wheel of thevehicle having traction increased due to the longitudinal load movement.Therefore, to ensure excellent vehicle braking performance, it ispreferable to enhance the component corresponding to the naturalfrequency of the suspension pitch motion in the regenerative brakingforce command so that load movement may be used.

In the present way, to enhance the component corresponding to thenatural frequency of the suspension pitch motion in the regenerativebraking force command, a filter configured for passing the componentcorresponding to the natural frequency may be configured and used.

At the present time, the filter may be a high-pass filter including acut-off frequency corresponding to the natural frequency of the transferfunction of the suspension pitch motion, a band-pass filter including acenter frequency corresponding to the natural frequency, etc.

In an exemplary embodiment of the present disclosure, because the filteris used to enhance, in the regenerative braking force command, acomponent corresponding to the natural frequency of the transferfunction of the pre-constructed suspension pitch motion, that is, thenatural frequency of the transfer function outputting the stateinformation related to the suspension pitch motion of the vehicle, asdescribed above, the cut-off frequency of the high-pass filter or thecenter frequency of the band-pass filter may not match a naturalfrequency to be passed.

However, the natural frequency to be passed needs to be higher than thecut-off frequency of the high-pass filter, and the natural frequency tobe passed needs to fall within the pass band of the band-pass filter.

In addition to the high-pass filter or the band-pass filter, amulti-dimensional filter may be used to enhance the componentcorresponding to the natural frequency. Furthermore, the filter may bedesigned using the transfer function itself constructed by modeling thereal-time vertical load caused by the above-described suspension pitchmotion or longitudinal load movement of the vehicle.

For example, it is assumed that a transfer function TF for deriving apitch angle (squat angle, φ) from an actual regenerative braking forcecommand (torque command, Tq) is constructed as in the following Equation3.

$\begin{matrix}{{TF} = {\frac{\phi}{Tq} = \frac{1}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}} & \left\lbrack {{Equation}3} \right\rbrack\end{matrix}$

In the instant case, a filter based on the transfer function TF may bedesigned and configured as illustrated in Equation 4 below, and may beapplied to the regenerative braking force command by the control unitand used to control the regenerative braking of the vehicle.

$\begin{matrix}\begin{matrix}{{{c_{4}sTF} + {c_{5}{TF}}} = {\frac{c_{4}s}{{c_{1}s^{2}} + {c_{2}s} + c_{3}} + \frac{c_{5}}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}} \\{= \frac{{c_{4}s} + c_{5}}{{c_{1}s^{2}} + {c_{2}s} + c_{3}}}\end{matrix} & \left\lbrack {{Equation}4} \right\rbrack\end{matrix}$

Here, c₁, c₂, c₃, c₄, c₅, etc. are coefficients which may be set(positive or negative), and s is a Laplace operator.

Previously, it has been described that a value of the natural frequencyused in the filter may be shifted according to the change in vehicleweight. A value of the natural frequency may be shifted by changingvalues of the Laplace operators c₁, c₂, c₃, c₄, and c₅ according to ashifted value.

FIG. 7 and FIG. 8 are diagrams for comparing a conventional wheel slipcontrol state with a regenerative braking control state of the presentdisclosure, and illustrate a regenerative braking control state for therear wheel and a regenerative braking control state for the front wheel,respectively.

In FIG. 7 , “the present disclosure” indicates a regenerative brakingcontrol state of the exemplary embodiment to which the natural frequencyremoval filter is applied, and in FIG. 8 “the present disclosure”indicates a regenerative braking control state of the exemplaryembodiment to which the natural frequency pass filter is applied.

In FIG. 7 , “rear wheel command torque before correction” indicates arear wheel torque (rear wheel regenerative braking torque or rear wheelregenerative braking force) command distributed from a required torque(required regenerative braking torque or required regenerative brakingforce) command according to the power distribution ratio. FIG. 7illustrates, as real-time change information, pitch angle informationduring vehicle dive (or nose-down), vertical load of the rear wheel,driving wheel (rear wheel) speed, vehicle speed, rear wheel torque (rearwheel regenerative braking torque) command before correction, and torque(regenerative braking torque) command after application of the filter,and indicates whether or not to start wheel slip control, etc.

According to a conventional control method, application of theregenerative braking torque command causes the vehicle to dive(nose-down), reducing the vertical load on the rear wheel. However, thevertical load is not simply reduced, and may be reduced while repeatedlydescending and ascending due to mechanical characteristics of thevehicle.

Accordingly, slip occurs so that the wheel speed momentarily increasesin the driving wheel (front wheel). When slip occurs, the wheel speedconverges while wheel slip control is performed, and occurrence of slip,performance of wheel slip control, and wheel speed convergence may berepeated again. As described above, according to the related art, asituation in which wheel slip control needs to be performed severaltimes may occur.

On the other hand, when the regenerative braking control methodaccording to an exemplary embodiment of the present disclosure isapplied, occurrence of wheel slip may be prevented in advance by use ofthe regenerative braking torque command after the filter is applied.Accordingly, wheel slip control may not be performed.

FIG. 8 illustrates pitch angle information during vehicle dive, rearwheel vertical load, deceleration, front wheel torque command beforecorrection, rear wheel torque command after addition, and a torquecommand after application of filter, and indicates whether wheel slipcontrol starts.

As may be seen from FIG. 8 , in an exemplary embodiment of the presentdisclosure, because a filter that enhances the natural frequencycomponent in the regenerative braking torque command is used, thevertical load on the front wheel increases, and the initial decelerationon the front wheel increases at the same time, so that initial brakingperformance of the vehicle may be increased.

Next, FIG. 9 , FIG. 10 and FIG. 11 are diagrams for describing an effectof regenerative braking control according to an exemplary embodiment ofthe present disclosure, FIG. 9 illustrates an effect of an exemplaryembodiment in which the filter for removing the natural frequencycomponent is applied, and FIG. 10 illustrates an effect of an exemplaryembodiment in which the filter for passing (enhancing) the naturalfrequency component is applied.

First, as illustrated in FIG. 9 , when regenerative braking forcecommand correction using a filter that removes or reduces thecorresponding natural frequency component from the regenerative brakingforce command and regenerative braking control according to theregenerative braking force command after correction are performed inconsideration of the natural frequency characteristics of the vehiclesuspension pitch motion (pitch motion), it is possible to performregenerative braking control configured for preventing or minimizingoccurrence of wheel slip before occurrence of wheel slip and not afteroccurrence of wheel slip. Furthermore, it is possible to performregenerative braking control configured for avoiding a region vulnerableto wheel slip when compared to regenerative braking control according tothe existing regenerative braking force command.

Furthermore, as illustrated in FIG. 10 , when regenerative braking forcecommand correction using a filter that enhances the correspondingnatural frequency component in the regenerative braking force commandand regenerative braking control according to the regenerative brakingforce command after correction are performed in consideration of thenatural frequency characteristics of the vehicle suspension pitch motion(pitch motion), it is possible to improve braking performance within alimit where wheel slip does not occur in consideration of real-timevertical load. That is, because it is possible to ensure and useadditional traction compared to regenerative braking control accordingto the existing regenerative braking force command, accelerationperformance may be increased.

Next, as illustrated in FIG. 11 , when regenerative braking forcecommand correction using a filter that removes or reduces thecorresponding natural frequency component from the regenerative brakingforce command and regenerative braking control according to theregenerative braking force command after correction are performed inconsideration of the natural frequency characteristics of the vehiclesuspension pitch motion, it is possible to attenuate excessivesuspension pitch motion of the vehicle. That is, it is possible toobtain an effect of attenuating the nose-up phenomenon when compared tothe regenerative braking control according to the existing regenerativebraking force command.

As a result, according to the regenerative braking control method of thepresent disclosure, it is possible to effectively prevent wheel sliponly by applying a software method without a change in vehicle hardwareor a cost increase factor, and it is possible to achieve increased tiredurability through wheel slip prevention. Furthermore, it is possible toobtain effects of improving the vehicle braking performance throughmaximum use of suspension pitch motion limit traction, and improvingride comfort due to the suspension pitch motion attenuation.

Accordingly, according to the method for controlling the regenerativebraking force of the vehicle according to an exemplary embodiment of thepresent disclosure, it is possible to effectively prevent wheel sliponly by applying a software method without a change in vehicle hardwareor a cost increase factor, and it is possible to achieve increased tiredurability through wheel slip prevention. Furthermore, it is possible toobtain effects of improving the vehicle braking performance throughmaximum use of suspension pitch motion limit traction, and improvingride comfort due to the suspension pitch motion attenuation.

Furthermore, the term related to a control device such as “controller”,“control apparatus”, “control unit”, “control device”, “control module”,or “server”, etc refers to a hardware device including a memory and aprocessor configured to execute one or more steps interpreted as analgorithm structure. The memory stores algorithm steps, and theprocessor executes the algorithm steps to perform one or more processesof a method in accordance with various exemplary embodiments of thepresent disclosure. The control device according to exemplaryembodiments of the present disclosure may be implemented through anonvolatile memory configured to store algorithms for controllingoperation of various components of a vehicle or data about softwarecommands for executing the algorithms, and a processor configured toperform operation to be described above using the data stored in thememory. The memory and the processor may be individual chips.Alternatively, the memory and the processor may be integrated in asingle chip. The processor may be implemented as one or more processors.The processor may include various logic circuits and operation circuits,may process data according to a program provided from the memory, andmay generate a control signal according to the processing result.

The control device may be at least one microprocessor operated by apredetermined program which may include a series of commands forcarrying out the method included in the aforementioned various exemplaryembodiments of the present disclosure.

The aforementioned invention can also be embodied as computer readablecodes on a computer readable recording medium. The computer readablerecording medium is any data storage device that can store data whichmay be thereafter read by a computer system and store and executeprogram instructions which may be thereafter read by a computer system.Examples of the computer readable recording medium include Hard DiskDrive (HDD), solid state disk (SSD), silicon disk drive (SDD), read-onlymemory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes,floppy discs, optical data storage devices, etc and implementation ascarrier waves (e.g., transmission over the Internet). Examples of theprogram instruction include machine language code such as thosegenerated by a compiler, as well as high-level language code which maybe executed by a computer using an interpreter or the like.

In various exemplary embodiments of the present disclosure, eachoperation described above may be performed by a control device, and thecontrol device may be configured by a plurality of control devices, oran integrated single control device.

In various exemplary embodiments of the present disclosure, the controldevice may be implemented in a form of hardware or software, or may beimplemented in a combination of hardware and software.

Furthermore, the terms such as “unit”, “module”, etc. included in thespecification mean units for processing at least one function oroperation, which may be implemented by hardware, software, or acombination thereof.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner”, “outer”, “up”, “down”,“upwards”, “downwards”, “front”, “rear”, “back”, “inside”, “outside”,“inwardly”, “outwardly”, “interior”, “exterior”, “internal”, “external”,“forwards”, and “backwards” are used to describe features of theexemplary embodiments with reference to the positions of such featuresas displayed in the figures. It will be further understood that the term“connect” or its derivatives refer both to direct and indirectconnection.

The foregoing descriptions of specific exemplary embodiments of thepresent disclosure have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit thepresent disclosure to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described toexplain certain principles of the present disclosure and their practicalapplication, to enable others skilled in the art to make and utilizevarious exemplary embodiments of the present disclosure, as well asvarious alternatives and modifications thereof. It is intended that thescope of the present disclosure be defined by the Claims appended heretoand their equivalents.

What is claimed is:
 1. A method for controlling regenerative braking ofa vehicle, the method comprising: determining a natural frequency ofvehicle suspension pitch motion according to characteristics of asuspension device of the vehicle; providing a filter configured forremoving or passing a natural frequency component of the vehiclesuspension pitch motion to a control unit of the vehicle; determining,by the control unit, a required regenerative braking force command basedon vehicle driving information collected during driving of the vehicle;determining, by the control unit, a final front wheel regenerativebraking force command and a final rear wheel regenerative braking forcecommand through a filtering process using the filter from the determinedrequired regenerative braking force command; and controlling, by thecontrol unit, a regenerative braking force applied to a front wheel anda rear wheel of the vehicle by a driving device for driving the vehicleaccording to the determined final front wheel regenerative braking forcecommand and the determined final rear wheel regenerative braking forcecommand.
 2. The method of claim 1, further including: constructing atransfer function modeled to determine and output state informationrelated to the vehicle suspension pitch motion by taking a variablerepresenting a vehicle driving state as input thereof, wherein thenatural frequency of the vehicle suspension pitch motion is determinedas a natural frequency of the constructed transfer function.
 3. Themethod of claim 1, wherein, in the filtering process, the filter isapplied to the required regenerative braking force command, a frontwheel regenerative braking force command distributed from the requiredregenerative braking force command, or a rear wheel regenerative brakingforce command distributed from the required regenerative braking forcecommand to remove or pass the natural frequency component of the vehiclesuspension pitch motion from or in the required regenerative brakingforce command, the front wheel regenerative braking force command, orthe rear wheel regenerative braking force command.
 4. The method ofclaim 1, wherein the filter is one selected from: a low-pass filterincluding a cut-off frequency corresponding to the natural frequency ofthe vehicle suspension pitch motion and a notch filter including acenter frequency corresponding to the natural frequency of the vehiclesuspension pitch motion, which are filters configured for removing thenatural frequency component; and a high-pass filter including a cut-offfrequency corresponding to the natural frequency of the vehiclesuspension pitch motion and a band-pass filter including the centerfrequency corresponding to the natural frequency of the vehiclesuspension pitch motion, which are filters configured for passing thenatural frequency.
 5. The method of claim 1, wherein the filter isconfigured for removing the natural frequency component of the vehiclesuspension pitch motion; and wherein the determining of the final frontwheel regenerative braking force command and the final rear wheelregenerative braking force command includes: distributing the requiredregenerative braking force command to a front wheel regenerative brakingforce command and a rear wheel regenerative braking force command todetermine a distributed front wheel regenerative braking force commandas the final front wheel regenerative braking force command; andapplying the filter to a distributed rear wheel regenerative brakingforce command to determine a rear wheel regenerative braking forcecommand after application of the filter as the final rear wheelregenerative braking force command.
 6. The method of claim 1, whereinthe filter is configured for removing the natural frequency component ofthe vehicle suspension pitch motion; and wherein the determining of thefinal front wheel regenerative braking force command and the final rearwheel regenerative braking force command includes: distributing therequired regenerative braking force command to a front wheelregenerative braking force command and a rear wheel regenerative brakingforce command; applying the filter to a distributed rear wheelregenerative braking force command to determine a rear wheelregenerative braking force command after application of the filter asthe final rear wheel regenerative braking force command; determining adifference between the distributed rear wheel regenerative braking forcecommand and the rear wheel regenerative braking force command afterapplication of the filter; and performing correction for compensating adistributed front wheel regenerative braking force command by thedetermined difference in command to determine a corrected front wheelregenerative braking force command as the final front wheel regenerativebraking force command.
 7. The method of claim 1, wherein the filter isconfigured for removing the natural frequency component of the vehiclesuspension pitch motion; and wherein the determining of the final frontwheel regenerative braking force command and the final rear wheelregenerative braking force command includes: applying the filter to therequired regenerative braking force command to determine the requiredregenerative braking force command after application of the filter; anddistributing the required regenerative braking force command afterapplication of the filter to a front wheel regenerative braking forcecommand and a rear wheel regenerative braking force command to determinea distributed front wheel regenerative braking force command and adistributed rear wheel regenerative braking force command as the finalfront wheel regenerative braking force command and the final rear wheelregenerative braking force command, respectively.
 8. The method of claim1, wherein the filter is configured for removing the natural frequencycomponent of the vehicle suspension pitch motion; and wherein thedetermining of the final front wheel regenerative braking force commandand the final rear wheel regenerative braking force command includes:applying the filter to the required regenerative braking force commandto determine the required regenerative braking force command afterapplication of the filter; distributing the required regenerativebraking force command after application of the filter to a front wheelregenerative braking force command and a rear wheel regenerative brakingforce command to determine a distributed rear wheel regenerative brakingforce command as the final rear wheel regenerative braking forcecommand; determining a difference between the required regenerativebraking force command before application of the filter and the requiredregenerative braking force command after application of the filter; andperforming correction for compensating a distributed front wheelregenerative braking force command by the determined difference incommand to determine a corrected front wheel regenerative braking forcecommand as the final front wheel regenerative braking force command. 9.The method of claim 1, wherein the filter is configured for removing thenatural frequency component of the vehicle suspension pitch motion; andwherein the determining of the final front wheel regenerative brakingforce command and the final rear wheel regenerative braking forcecommand includes: distributing the required regenerative braking forcecommand to a front wheel regenerative braking force command and a rearwheel regenerative braking force command; applying the filter to therequired regenerative braking force command to determine the requiredregenerative braking force command after application of the filter;distributing the required regenerative braking force command afterapplication of the filter to a front wheel regenerative braking forcecommand and a rear wheel regenerative braking force command; anddetermining a distributed rear wheel regenerative braking force commanddistributed from the required regenerative braking force command afterapplication of the filter and a distributed front wheel regenerativebraking force command distributed from the required regenerative brakingforce command before application of the filter as the final rear wheelregenerative braking force command and the final front wheelregenerative braking force command, respectively.
 10. The method ofclaim 1, wherein the filter is configured for removing the naturalfrequency component of the vehicle suspension pitch motion; and whereinthe determining of the final front wheel regenerative braking forcecommand and the final rear wheel regenerative braking force commandincludes: distributing the required regenerative braking force commandto a front wheel regenerative braking force command and a rear wheelregenerative braking force command; applying the filter to the requiredregenerative braking force command and determining the requiredregenerative braking force command after application of the filter;determining a difference between the required regenerative braking forcecommand before application of the filter and the required regenerativebraking force command after application of the filter; and performingcorrection for compensating each of a distributed front wheelregenerative braking force command and a distributed rear wheelregenerative braking force command by the determined difference incommand to determine the final front wheel regenerative braking forcecommand and the final rear wheel regenerative braking force command froma corrected front wheel regenerative braking force command and acorrected rear wheel regenerative braking force command, respectively.11. The method of claim 1, wherein the filter is configured for passingthe natural frequency component of the vehicle suspension pitch motion;and wherein the determining of the final front wheel regenerativebraking force command and the final rear wheel regenerative brakingforce command includes: distributing the required regenerative brakingforce command to a front wheel regenerative braking force command and arear wheel regenerative braking force command to determine a distributedrear wheel regenerative braking force command as the final rear wheelregenerative braking force command; applying the filter to a distributedfront wheel regenerative braking force command to determine the frontwheel regenerative braking force command after application of thefilter; and adding the front wheel regenerative braking force commandafter application of the filter to the distributed front wheelregenerative braking force command distributed from the requiredregenerative braking force command to determine the front wheelregenerative braking force command after addition as the final frontwheel regenerative braking force command.
 12. The method of claim 1,wherein the filter is configured for passing the natural frequencycomponent of the vehicle suspension pitch motion; and wherein thedetermining of the final front wheel regenerative braking force commandand the final rear wheel regenerative braking force command includes:distributing the required regenerative braking force command to a frontwheel regenerative braking force command and a rear wheel regenerativebraking force command; applying the filter to a distributed front wheelregenerative braking force command to determine the front wheelregenerative braking force command after application of the filter asthe final front wheel regenerative braking force command; andsubtracting the front wheel regenerative braking force command afterapplication of the filter from a distributed rear wheel regenerativebraking force command distributed from the required regenerative brakingforce command to determine the rear wheel regenerative braking forcecommand after subtraction as the final rear wheel regenerative brakingforce command.
 13. The method of claim 1, wherein the filter isconfigured for passing the natural frequency component of the vehiclesuspension pitch motion; and wherein the determining of the final frontwheel regenerative braking force command and the final rear wheelregenerative braking force command includes: distributing the requiredregenerative braking force command to a front wheel regenerative brakingforce command and a rear wheel regenerative braking force command;applying the filter to a distributed rear wheel regenerative brakingforce command to determine the rear wheel regenerative braking forcecommand after application of the filter as the final rear wheelregenerative braking force command; and adding the rear wheelregenerative braking force command after application of the filter to adistributed front wheel regenerative braking force command distributedfrom the required regenerative braking force command to determine thefront wheel regenerative braking force command after addition as thefinal front wheel regenerative braking force command.
 14. The method ofclaim 1, wherein the filter is configured for passing the naturalfrequency component of the vehicle suspension pitch motion; and whereinthe determining of the final front wheel regenerative braking forcecommand and the final rear wheel regenerative braking force commandincludes: distributing the required regenerative braking force commandto a front wheel regenerative braking force command and a rear wheelregenerative braking force command to determine a distributed frontwheel regenerative braking force command as the final front wheelregenerative braking force command; applying the filter to a distributedrear wheel regenerative braking force command to determine the rearwheel regenerative braking force command after application of thefilter; and subtracting the rear wheel regenerative braking forcecommand after application of the filter from the distributed rear wheelregenerative braking force command distributed from the requiredregenerative braking force command to determine the rear wheelregenerative braking force command after subtraction as the final rearwheel regenerative braking force command.
 15. The method of claim 1,wherein the filter is configured for passing the natural frequencycomponent of the vehicle suspension pitch motion; and wherein thedetermining of the final front wheel regenerative braking force commandand the final rear wheel regenerative braking force command includes:distributing the required regenerative braking force command to a frontwheel regenerative braking force command and a rear wheel regenerativebraking force command; applying the filter to the required regenerativebraking force command to determine the required regenerative brakingforce command after application of the filter; and performing correctionfor compensating each of a distributed front wheel regenerative brakingforce command and a distributed rear wheel regenerative braking forcecommand by the required regenerative braking force command afterapplication of the filter to determine a corrected front wheelregenerative braking force command and a corrected rear wheelregenerative braking force command as the final front wheel regenerativebraking force command and the final rear wheel regenerative brakingforce command, respectively.
 16. The method of claim 1, wherein thefilter is configured for passing the natural frequency component of thevehicle suspension pitch motion; and wherein the determining of thefinal front wheel regenerative braking force command and the final rearwheel regenerative braking force command includes: distributing therequired regenerative braking force command to a front wheelregenerative braking force command and a rear wheel regenerative brakingforce command; applying the filter to the required regenerative brakingforce command to determine the required regenerative braking forcecommand after application of the filter; distributing the requiredregenerative braking force command after application of the filter as afront wheel distribution component and a rear wheel distributioncomponent; adding the front wheel distribution component to adistributed front wheel regenerative braking force command to determinethe front wheel regenerative braking force command after addition as thefinal front wheel regenerative braking force command; and subtractingthe rear wheel distribution component from a distributed rear wheelregenerative braking force command to determine the rear wheelregenerative braking force command after subtraction as the final rearwheel regenerative braking force command.
 17. The method of claim 1,further including: estimating, by the control unit, a vehicle weightbased on information collected through an in-vehicle sensor; andchanging, by the control unit, the filter so that a natural frequencyallowed to be removed or passed by the filter is shifted according to achange amount of the estimated vehicle weight.
 18. The method of claim1, wherein the determining of the final front wheel regenerative brakingforce command and the final rear wheel regenerative braking forcecommand includes determining, by the control unit, whether to apply thefilter based on the vehicle driving information, and wherein upondetermining not to apply the filter from the vehicle drivinginformation, a front wheel regenerative braking force command and a rearwheel regenerative braking force command obtained by distributing therequired regenerative braking force command according to a powerdistribution ratio are determined as the final front wheel regenerativebraking force command and the final rear wheel regenerative brakingforce command without the filtering process.
 19. The method of claim 1,wherein the control unit is configured to: determine a weightcorresponding to a current vehicle driving state using a state variablemap from the vehicle driving information; and adjust gain of the filteraccording to the determined weight.
 20. The method of claim 1, whereinthe determining of the final front wheel regenerative braking forcecommand and the final rear wheel regenerative braking force commandincludes: determining weights α and 1×α corresponding to a currentvehicle driving state using a state variable map from the vehicledriving information; distributing the required regenerative brakingforce command according to a power distribution ratio to determine afront wheel regenerative braking force command and a rear wheelregenerative braking force command; adding values obtained by applyingthe determined weights α and 1−α to a front wheel regenerative brakingforce command determined without the distribution and filtering processand a front wheel regenerative braking force command obtained throughthe filtering process after the distribution; adding values obtained byapplying the determined weights α and 1−α to a rear wheel regenerativebraking force command determined without the distribution and filteringprocess and a rear wheel regenerative braking force command obtainedthrough the filtering process after the distribution; and determiningthe front wheel regenerative braking force command and the rear wheelregenerative braking force command obtained by addition afterapplication of the weights as the final front wheel regenerative brakingforce command and the final rear wheel regenerative braking forcecommand.